The following definitions have been taken from Wikipedia.
Some have been summarised of modified slightly by myself.
Active
Describes a piece that is able to move or control many squares.
Adjust or j’adoube
To adjust the position of a piece on its square without being required to move it. Adjustment can only be done when it is the player’s move and the adjustment is preceded by saying “I adjust” or “j’adoube”.
Algebraic notation
The standard way to record a chess game using alphanumeric coordinates for the squares.
K = King
Q = Queen
N = Knight
B = Bishop
O-O = Castle Kingside
O-O-O = Castle Queenside
+ = Check
# = Checkmate
Pawn moves – When there is only a small letter and a number it is always a pawn move.For example e4 = Pawn moving to the e4 sqaure.
The result – The result is shown by 1-0 with white winning or 0-1 with black winning or 1/2-1/2 indicating a draw.
Analysis
Study of a position to determine best play for both sides.
Annotation
Commentary on a game using a combination of written comments, chess symbols or notation.
Arbiter
A tournament official who arbitrates disputes and ensures the rules of the tournament and game of chess are kept by the players.
Back rank
A player’s first rank (the one on which the pieces stand in the initial array); White’s back rank is Black’s eighth rank, and vice versa.
Back-rank mate
A checkmate delivered by a rook or queen along a back rank in which the mated king is unable to move up the board because the king is blocked by friendly pieces (usually pawns) on the second rank. This is also sometimes referred to as a back-row mate.
Backward pawn
A pawn that is behind the pawns of the same color on the adjacent files and that cannot be advanced with the support of another pawn.
Bad bishop
A bishop which is hemmed in by the player’s own pawns.
Bind
A strong grip or stranglehold on a position that is difficult for the opponent to break. A bind is usually an advantage in space created by advanced pawns. The Maróczy Bind is a well-known example.
Blitz chess
A fast form of chess (Blitz being German for lightning) with a very short time limit.
Blockade
A strategic placement of a minor piece directly in front of an enemy pawn, where it restrains the pawn’s advance and gains shelter from attack.
Blunder
A very bad move, an oversight
Indicated by “?” (a bad move) or “??” (a very bad move).
Book move
An opening move found in the standard reference books on opening theory. A game is said to be “in book” when both players are playing moves found in the opening references. A game is said to be “out of book” when the players have reached the end of the variations analyzed in the opening books or if one of the players deviates with a novelty (or a blunder).
Bughouse chess or Transfer Chess
A chess variant played with teams of two or more.
Bullet chess
A form of chess in which each side has 1 minute to make all their moves.
Bye
A tournament round in which a player does not have a game, usually because there are an odd number of players. A bye is normally scored as a win (1 point), although in some tournaments a player is permitted to choose to take a bye (usually in the first or last round) and score it as a draw (½ point).
Calculate
To carefully plan a series of moves while considering possible responses.
Capture
Remove the opponent’s piece or pawn from the board by taking it with one’s own piece or pawn. Except in the case of an en passant capture, the capturing piece or pawn does so by occupying the same square that the captured piece or pawn occupied.
Castling
A special move involving both the king and one rook. Its purpose is generally to protect the king and develop the rook. Castling on the kingside is sometimes called castling short and castling on the queenside is called castling long; the difference is based on whether the rook moves a short distance (two squares) or a long distance (three squares).
The algebraic notation for kingside castling is O-O.
The algebraic notation for queenside Castling is O-O-O.
Check
An attack on the king. The attacked king is said to be in check.
Checkmate
A position in which a player’s king is in check and the player has no legal move (i.e cannot move out of check). A player whose king is checkmated loses the game.
Chess960
A chess variant with a randomized positioning of non-pawn pieces to start the game.
Chessboard
This is the chequered board used in chess. It consists of 64 squares (eight rows and eight columns) arranged in two alternating colors (light and dark).
Chess clock
A device made up of two adjacent clocks and buttons, keeping track of the total time each player takes for their moves. Immediately after moving, the player hits his button, which simultaneously stops his clock and starts his opponent’s. The picture shown displays an analogue clock where the term ‘flag fall’ originates. Modern clocks are digital.
Closed position
A position with few open lines (files or diagonals), generally characterized by interlocking pawn chains, cramped positions with few opportunities to exchange, and extensive maneuvering behind lines. Such a position may later become an Open game.
Compensation
An imbalanced equivalent return, for example sacrificing material for development or trading a bishop for three pawns.
Connected pawns
Refers to two or more pawns of the same color on adjacent files.
Connected passed pawns
Passed pawns on adjacent files. These are considered to be unusually powerful (often worth a minor piece or rook if on the sixth rank or above and not properly blockaded) because they can advance together. Also see connected pawns.
Connected rooks
Two rooks of the same color on the same rank or file with no pawns or pieces between them. Connected rooks are usually desirable. Players often connect rooks on their own first rank or along an open file. cf. Doubled rooks.
Control of the center
Having one or more pieces that attack any of the four center squares; an important strategy, and one of the main aims of openings.
Correspondence chess
This is chess played at a long time control by various forms of long-distance correspondence, usually through a correspondence chess server, through email or by the postal system. Typically, one move is transmitted in every correspondence.
Countergambit
A gambit offered by Black, for example the Greco Counter Gambit, usually called the Latvian Gambit today (1.e4 e5 2.Nf3 f5?!); the Albin Countergambit (1.d4 d5 2.c4 e5); and theFalkbeer Countergambit (1.e4 e5 2.f4 d5). An opening need not have “countergambit” in its name to be one; for instance, the Benko Gambit (1.d4 Nf6 2.c4 c5 3.d5 b5), Englund Gambit (1.d4 e5?), the Budapest Gambit (1.d4 Nf6 2.c4 e5), the Blackburne Shilling Gambit (1.e4 e5 2.Nf3 Nc6 3.Bc4 Nd4?!) and many lines of the Two Knights Defense (e.g. 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 and now 4…Bc5!? (the Wilkes-Barre Variation or Traxler Counter-Attack), 4…Nxe4?!, 4…d5 5.exd5 Na5 6.Bb5+ c6 (the main line), 4…d5 5.exd5 Nd4 (the Fritz Variation), and 4…d5 5.exd5 b5 (the Ulvestad Variation)) are all examples of countergambits.
Counterplay
Active maneuvering by the player in an inferior or defensive position.
Cramped
A position with limited mobility.
Diagonal
A line of squares of the same colour touching corner to corner, along which a queen or bishop can move.
Discovered attack
An attack made by a queen, rook or bishop when another piece or pawn moves out of its way.
Discovered check
A discovered attack to the king.
Doubled pawns
A pair of pawns of the same color on the same file.
Doubled rooks
Two of a player’s rooks placed on the same file or rank.
Draw
A game that ends without victory for either player. Most drawn games are draws by agreement. The other ways that a game can end in a draw are stalemate, threefold repetition, the fifty-move rule, and insufficient material. A position is said to be a draw (or a “drawn position” or “theoretical draw”) if either player can, through correct play, eventually force the game into a position where the game must end in a draw, regardless of the moves made by the other player. A draw is usually scored as ½ point, although in some matches only wins are counted and draws are ignored.
Drawish
An adjective describing a position or game that is likely to end in a draw.
Elo rating system
The Elo rating system is a method for calculating the relative skill levels of chess players, named after the Hungarian Arpad Elo. Since 1970 FIDE publishes quarterly an international chess rating list using the Elo system.
En passant
(“in the act of passing”; derived from French) The rule that allows a pawn that has just advanced two squares to be captured by a pawn on the same rank and adjacent file. The pawn is therefore taken as if it had only moved one space. It is only possible to take en passant on the next move.
En prise
En prise describes a piece or pawn exposed to a material winning capture by the opponent. This is either a hanging piece, an undefended pawn, a piece attacked by a less valuable attacker, or a piece or pawn defended insufficiently. For instance, after 1.e4 Nf6 2.Nf3? leaves White’s e-pawn en prise.
Endgame
The stage of the game when there are few pieces left on the board. The endgame follows the middlegame.
Equalise
To create a position where the players have equal chances of winning (referred to as “equality”). This may be either “static equality”, where a draw is likely (for example, a balanced endgame) or even certain (for example, by perpetual check), or “dynamic equality”, where White and Black have equal chances of winning the game. In opening theory, since White has the advantage of the first move, lines that equalize are relatively good for Black and bad for White.
Fianchetto
Refers to a bishop developed to the second square and the longest diagonal on the file of the adjacent knight (that is, b2 or g2 for white, b7 or g7 for black), or the process of developing a bishop to such a square. It usually occurs after moving the pawn on that file ahead one square (or perhaps two). The Italian word is actually a noun (“in fianchetto”) and not a verb.
FIDE
The World Chess Federation (Fédération Internationale des Échecs), the primary international chess organizing and governing body. The abbreviated name FIDE is nearly always used in place of the full name in French.
FIDE Master (FM)
A chess title ranking below International Master.
Fifty-move rule
A draw may be claimed if no capture or pawn move has occurred in the last fifty moves by either side.
File
A column of the chessboard. A specific file can be named either using its position in algebraic notation, a–h, or by using its position indescriptive notation. For example, the f-file or the king bishop file comprises the squares f1–f8.
Flag
Part of an analogue chess clock (usually red) which indicates when the minute hand passes the hour. To flag someone means winning the game on the basis of the opponent exceeding the time control.
Flank
The queenside a, b, and c-files, or the kingside f, g, and h-files, also called wing; distinguished from the center d and e-files.
Forced move
A move which is the only one which does not result in a serious disadvantage for the moving player. “Forced” can also be used to describe a sequence of moves for which the player has no viable alternative, e.g. “the forced win of a piece” or “a forced checkmate”. In these cases the player cannot avoid the loss of a piece or checkmate, respectively.
Forfeit
Refers to losing the game by absence or by exceeding the time control (forfeit on time).
Fork
When one piece, generally a knight or pawn, simultaneously attacks two (or more) of the opponent’s pieces, often specifically called a knight fork when the attacker is a knight. Some sources state that only a knight can give a fork and that the term double attack is correct when another piece is involved, but this is by no means a universal usage.
Gambit
A sacrifice (usually of a pawn) used to gain an early advantage of space and /or time in the opening.
Grandmaster (GM)
The highest title a chess player can attain (besides World Champion). When used precisely, it is the title awarded by FIDE starting in 1950, but it can be used to describe someone of comparable ability.
Hanging
Unprotected and exposed to capture. It is not the same as en prise since a piece en prise may be protected. To “hang a piece” is to lose it by failing to move or protect it.
Hole
A square that a player does not, and cannot in future, control with a friendly pawn. The definition is somewhat subjective: the square must have some positional significance for the opponent to be considered a hole – squares on the first and second ranks are not holes. On the other hand a square is a hole even if it can be controlled in the future with a pawn that has made a capture. An example of the hole is the square e4 in the Stonewall Attack.
Illegal move
A move that is not permitted by the rules of chess. An illegal move discovered during the course of a game is to be corrected.
Increment
An increment refers to the amount of time added to each player’s time before each move. For instance rapid chess might be played with “25 minutes plus 10 second per move increment”, meaning that each player starts with 25 minutes on their clock, and this increments by 10 seconds after (or before) each move, usually using the Fischer Delay method.
Insufficient material
An endgame scenario in which all pawns have been captured, and one side has only its king remaining while the other is down to just a king, a king plus one knight, a king plus one bishop, or indeed a king plus any number of bishops on the same colour as each other (up to nine), as is possible via underpromotion. A king and bishop versus a king and bishop with the bishops on the same color is also a draw. The position is a draw because it is impossible for the dominant side to deliver checkmate regardless of play. Situations where checkmate is possible only if the inferior side blunders are covered by the fifty-move rule.
International Master (IM)
A chess title that ranks below Grandmaster but above FIDE Master.
Isolated pawn
A pawn with no pawn of the same color on an adjacent file.
Main line
The principal, most important, or most often played variation of an opening or piece of analysis. For example, 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.Nf3 0-0 6.Be2 e5 7.0-0 Nc6 8.d5 Ne7 is often referred to as the main line of the King’s Indian Defence.
Maróczy Bind
A bind on the light squares in the center, particularly d5, obtained by White by placing pawns on c4 and e4. Named for Géza Maróczy, it originally referred to formations arising in some variations of the Sicilian Defence, but the name is now also applied to similar setups in the English Opening and the Queen’s Indian Defence. It was once greatly feared by Black but means of countering it have been developed since the 1980s and earlier.
Material
All of a player’s pieces and pawns on the board. The player with pieces and pawns of greater value is said to have a “material advantage”. When a player gains a material advantage they are also said to be “winning material”.
Middlegame
The part of a chess game that follows the opening and comes before the endgame, beginning after the pieces are developed in the opening. This is usually roughly moves 20 through 40.
Minor piece
A bishop or knight.
Move order
The sequence of moves one chooses to play an opening or execute a plan. Different move orders often have different advantages and disadvantages. For example, 1.d4 Nf6 2.Nf3 avoids the Budapest Gambit (2.c4 e5!?), but makes it impossible for White to play the Sämisch Variation (2.c4 g6 3.Nc3 Bg7 4.e4 d6 5.f3) or Four Pawns Attack (5.f4) against theKing’s Indian Defence, and to transpose to certain lines of the Nimzo-Indian Defence and Queen’s Gambit Declined, Exchange Variation where the knight goes to e2 instead of f3.
Norm
A performance at a chess tournament that indicates a player is ready to receive a title, or the level of performance needed. In addition to other requirements, a certain number of norms is generally required to earn a title.
Open position
A position in which exchanges have opened files and diagonals, as opposed to a closed game.
Opening
The beginning moves of the game, roughly the first 10-20 moves. In the opening players set up their pawn structures, develop their pieces, and typically castle. The opening precedes the middlegame.
Opening preparation
Home study and analysis of openings and defenses that one expects to play, or meet, in later tournament or match games. In high-level play, an important part of this is the search for theoretical novelties that improve upon previous play or previously published analysis.
Opening repertoire
The set of openings played by a particular player. The breadth of different players’ repertoires varies from very narrow to very broad. For example, a player who always opens with 1.e4; always meets 1.e4 with the Sicilian Defence, and the Najdorf Variation of it if allowed; and always meets 1.d4, 1.c4, or 1.Nf3 with 1…f5, intending to play the Dutch Defence, has a very narrow opening repertoire. Bent Larsen, who opened at various times with 1.e4, 1.d4, 1.c4, 1.f4, 1.Nf3, 1.b3, and 1.g3, and played a large number of different defenses as Black, had a very broad opening repertoire.
Outpost
An outpost is a square protected by a pawn that is in or near the enemy’s stronghold. Outposts are a favourable position from which to launch an attack, particularly using a knight.
Passed pawn
A pawn that has no pawn of the opposite color on its file or on any adjacent files on its way to queening.
Passive
A piece that is able to move to or control relatively few squares, also referred to as an inactive piece.
Pawn center
A player has a pawn centre when he has several pawns in the centre. By extension, pawns on the squares adjacent to the centre may also be considered as part of the pawn centre. Having an ample pawn centre as the one on the diagram at right was considered a huge advantage until the hypermodernist school nuanced this judgment. See King’s Indian Defence, Four Pawns Attack for an example of an opening leading to an extended pawn center.
Pawn chain
A locked diagonal formation of pawns, each one supported by a friendly pawn diagonally behind and blocked by an enemy pawn directly ahead. Nimzowitsch considered pawn chains extensively, and recommended attacking the enemy pawn chain at its base. See pawn structure.
Pawn island
A group of pawns of one color on consecutive files with no other pawns of the same color on any adjacent files. A pawn island consisting of one pawn is called an isolated pawn.
Pawn storm
An attacking technique where a group of pawns on one wing is advanced to break up the defence.
Pawn structure
The placement of the pawns is known as the pawn structure. As pawns are the least mobile of the pieces and the only pieces unable to move backwards, the position of the pawns greatly influences the character of the game.
Perpetual check
A draw forced by one player putting the opponent’s king in a potentially endless series of checks.
Pin
When a piece can not move (either legally or advisedly) because doing so would expose a valuable piece, usually the king or queen, to attack. Pins against the king are calledabsolute because it is then illegal to move the pinned piece.
Poisoned Pawn
An unprotected pawn which, if captured, causes positional problems or material loss. It is also a variation of the Najdorf Variation of theSicilian Defence, where some players call White’s pawn on b2 a poisoned pawn since it is dangerous for Black to capture it.
Portable Game Notation (PGN)
This is a popular computer-processible ASCII format for recording chess games (both the moves and related data).
Promotion
Advancing a pawn to the eighth rank, converting it to a queen, rook, bishop or knight. Promotion to a piece other than a queen is called underpromotion.
Rank
A row of the chessboard. Specific ranks are referred to by number, first rank, second rank, …, eighth rank. Unlike the case with files, rank names are always given from the point of view of each individual player, with the first rank being the home row of the king and other pieces. White’s first rank is Black’s eighth rank (row 1) and White’s eighth is Black’s first (row 8), White’s second rank is Black’s seventh rank (row 2) and White’s seventh is Black’s second (row 7), and so on.
Resign
To concede loss of the game. A resignation is usually indicated by stopping the clocks, and sometimes by offering a handshake or saying “I resign”. The traditional way to resign is by tipping over one’s king, but this is rarely done nowadays. In published games, a player’s resignation is often indicated by “1–0” (Black resigns) or “0–1” (White resigns); these may also indicate that the game was decided for some other reason, usually one side exceeding the time control. In master and serious amateur play, it is much more common for a game to be resigned than for it to end with checkmate, because players can foresee checkmate well in advance.
Round-robin tournament
This is a tournament in which each participant plays every other participant an equal number of times. In a double round-robin tournament the participants play each other exactly twice, once with white and once with black. An example of the former is the Hastings 1895 chess tournament, an example of the latter is the Piatigorsky Cup. This type of tournament is commonly used if the number of participants is relatively small. See also Swiss system tournament.
Sac
Short for sacrifice, usually used to describe a sacrifice for a mating attack.
Sacrifice
When one player voluntarily gives up material in return for an advantage such as space, development, or an attack. A sacrifice in the opening is called a gambit.
Simplification
A strategy of exchanging pieces of equal value. Simplification can be used defensively to reduce the size of an attacking force. It can also be used by a player with an advantage to amplify that advantage or reduce the opponent’s counterplay. Simplification is also used as an attempt to obtain a draw, or as an attempt to gain an advantage by players who are strong in endgame play with simplified positions. Also liquidation and trading.
Simultaneous chess
A form of chess in which one (usually expert) player plays against several (usually novice) players simultaneously. Is often an exhibition.
Skewer
An attack to a valuable piece, compelling it to move to avoid capture and thus exposing a less valuable piece which can then be taken.
Stalemate
A position in which the player whose turn it is to move has no legal move and his king is not in check. A stalemate results in an immediate draw.
Strategy
Evaluation of game positions and setting up goals and longer-term plans for future play, as opposed to a tactic which is a shorter-term plan typically consisting of a well-defined sequence of moves and their contingent moves from a given position in a game.
Symmetry
A symmetrical position on the chessboard means the positions of one’s pieces are exactly mirrored by the opponent’s pieces. This most often occurs when Black mimics White’s opening moves. Black is said to break symmetry when he makes a move no longer imitating White’s move.
Tempo
An extra move, an initiative at development. A player gains a tempo (usually in the opening) by making the opponent move the same piece twice or defend an enemy piece. In the endgame, one may wish to lose a tempo by triangulation to gain the opposition. (Plural: tempos or tempi).
Threefold repetition
A draw may be claimed if the same position occurs three times with the same player to move, and with each player having the same set of legal moves each time (the latter includes the right to take en passant and the right to castle).
Touch-move rule
The rule requiring a player who touches a piece that has at least one legal move to move that piece (and, if the player moves the piece to a particular square and takes his hand off it, to move it to that square). Castling must be initiated by moving the king first, so a player who touches his rook may be required to move it, without castling. The rule also requires a player who touches an opponent’s piece to capture it if possible. A player wishing to touch a piece to adjust its position on a square without being required to move it signals this intent by saying “J’adoube” or “I adjust”.
Transposition
Arriving at a position using a different sequence of moves.
Trap
A move which may tempt the opponent to play a losing move.
Trébuchet
A position of mutual zugzwang in which either player would lose if it is their turn to move.
Variation
A sequence of moves or alternative line of play, often applied to the opening. A variation does not have to have been played in a game, it may also be a possibility that occurs only in analysis. The word Variation is also used to name specific sequences of moves within an opening. For an example, the Dragon Variation is part of the Sicilian Defence.
Weak square
A square that cannot be easily defended from attack by an opponent. Often a weak square is unable to be defended by pawns (a hole) and can be theoretically occupied by a piece. Exchange or loss of a bishop may make all squares of that bishop’s color weak resulting in a “weak square complex” on the light squares or the dark squares.
Windmill
A combination in which two pieces work together to deliver an alternating series of checks and discovered checks in such a way that the opposing king is required to move on each turn. It is a potent technique since on every other move, the discovered check may allow the non-checking piece to capture an enemy piece without losing a tempo.
Zugzwang
(from the German) When a player is put at a disadvantage by having to make a move; where any legal move weakens the position. Zugzwang usually occurs in the endgame, and rarely in the middlegame.
Zwischenzug
(from the German) An “in-between” move played before the expected reply.