Accept~To take an offered piece. 
Active~An aggressive move, line of play, or position. 
Active defense~The use of attack as a defense, rather than passively trying to cover weaknesses.
Active piece~A developed piece that is actively participating in the conduct of the game. 
Advantage~Where the current position of the game favours one side over another. 
Alertness~The ability to take advantage of the opponent's inaccuracies while playing accurately yourself.
Algebraic notation~The modern way of recording chess moves.
Alpha-Beta pruning~A technique used by computer programmers to cut down on the number of possible moves a computer has to evaluate.
Analysis~the calculation of possible moves and variations for a position.
Annotation~a written comment about a game or position. May include variations from the main line of play.
Artificial castling~exchanging the positions of the king and rook other than by castling.
Artificial manoeuvre~Trying a bit too hard, or making an odd use of pieces.
Attack~ An aggressive move threatening the capture of a piece or pawn or an empty square.
Back rank~The first rank on the board for each player. 
Backward pawn~ A pawn at the base of a pawn chain that can't move forward due to one or more enemy pawns on the adjacent files.
Bad bishop~A bishop whose movement is restricted by friendly pawns on its colour squares. 
Base of pawn chain~The very last pawn in a diagonal chain, the weakest point due to it not being supported by another pawn.
Battery~A lineup of pieces that move similarly on a single file or diagonal, usually pointing toward a critical point in the enemy's camp.
Berserker~A rash playing style characterized by frenzied attacking with one or two pieces, perhaps with little regard for strategy or danger.
Bind~Where a player is so tied up he has trouble finding useful moves. 
Bishop pair~when two bishops are effective together because they control diagonals of both colours, and work very well in open positions.
Blockade~Immobilization of an enemy pawn by placing a piece on the square directly in front of it.
Blockading square~The square directly in front of an isolated or backward pawn. 
Blunder~A horrible mistake where material is lost, serious tactical or positional concessions are made, or the game is lost.
Book~Published opening theory.
Book Player~A person who memorizes opening theory. 
Break~A pawn move that proposes a pawn trade in order to increase space or relieve a cramped position.
Breakthrough~Penetrating the enemy's position, whether by a pawn break or the sacrifice of pieces or pawns.
Brilliancy~A game containing a very deep strategic idea, a beautiful combination, or an original idea or plan.
Broad pawn centre~Three or four centre pawns abreast, which indicate very aggressive intentions.
Buried piece~A piece hemmed in by friendly pieces and pawns.
Calculation~The working out of variations mentally, without moving the pieces.
Candidate move~A move considered as a starting point in the analysis of variations.
Capped pawn~A marked pawn with which a player engages to deliver checkmate, in giving extreme odds to a weaker opponent.
Capture~Moving a piece to a square occupied by an enemy piece, thereby removing the enemy piece from the board, out of play.
Castle~ The act of moving the king and rook simultaneously. 
Castle long~Queenside castling.
Castle short~Kingside castling.
Centralisation~To move pieces towards the centre.
Centre break~The attack on two or more pawns abreast on the 4th rank by an opposing pawn in order to break up their formation.
Centre pawns~The king's and queen's pawns.
Centralize~Placing of pieces and pawns so they both control the centre, and influence other areas of the board.
Check~The act of attacking the opponent's king. 
Checkmate~Threatening the capture of the enemy king such that it cannot escape.
Classical~A playing style based on the formation of a full pawn centre.
Clearance~A move that clears a square for use by a different piece. 
Closed game~A position where the pawn structure is fixed, the centre cluttered with interlocked pawns. 
Combination~A sacrifice and forced sequence of moves to gain a certain advantage.
Compensation~An equivalent advantage that offsets an advantage of the enemy's, for example material vs. development.
Connected passed pawns~Two or more same-colour passed pawns on adjacent files. 
Connected rooks~When the two rooks are on the same rank or file, with no pieces or pawns between them.
Consolidate~Taking care of your position before continuing active operations. 
Control~The domination or sole use of a square, group of squares, file ordiagonal.
Coordinate~a unique square identifiers, made up of a number indicating rank and a letter indicating file.
Counter attack~The launch of an attack by the defender, rather than making more defensive moves. 
Cramped~a disadvantage in space, leading to a reduction in mobility of one's pieces.
Cross-check~A check in reply to a check.
Decisive~A move which alters or makes certain the result of a game. 
Decline~To not take an offered piece.
Decoy~ The offering of material in order to get an enemy piece to move.
Defense~ Any move or plan that is intended to meet or stop an enemy's threats or attack.
Deflection~A tactic which forces an opponent piece from a square, either because it was defending a piece or square blocking a threat.
Destructive sacrifice~Sacrificing material to destroy the pawn cover or other protection around the enemy king.
Development~The moving of pieces from their starting positions to new positions where their mobility and activity are increased.
Diagonal~A diagonal row of squares.
Discovered attack~The creation of an attack from one piece caused by the moving away of another piece that was masking it.
Discovered check~the check given by one piece as the result of the moving away of another piece that was masking it.
Dislodging manoeuvre~A move to upset a defensive formation.
Distance~The number of squares between two pieces.
Double attack~The launch of two threats simultaneously.
Double check~A simultaneous check given by moving one piece to give check, thereby also unmasking another piece which also gives check.
Doubled pawns~Two pawns of the same colour on the same file, put there by a capture.
Draw~A game that ends in a tie, where each player is awarded half a point. 
Draw offer~The suggestion by one player to the other that they agree to call the game a draw.
Elo rating~An internationally accepted mathematical system for ranking chess players.
Endgame~The final phase of the game when there are few pieces left on the board.
En passant~the term to describe when a pawn moves two squares from its starting position, and passes an enemy pawn. 
En prise~A piece or pawn that is unprotected and exposed to capture.
Equality~Where neither player has a discernible advantage over the opponent.
Exchange~A trade of pieces. 
Exchange sacrifice~Where a player willfully trades a rook for a minor piece in return for compensation of some kind.
Expansion~Increasing the amount of space directly under your control.
Fianchetto~The development of a bishop to b2 or g2, b7 or g7 for Black.
FIDE~Federation Internationale des Echecs, the world governing body for chess. 
Fifty move rule~where a game can be drawn when fifty moves have been made by each player without a capture or pawn advancement.
File~A row of eight squares from one end of the chessboard to the other.
Fixed centre~Where the centre of the board is occupied by multiple pawns and some of them are fixed in place by opposing pawns.
Fixed pawn structure~Pawn set-ups where there is little or no possible mobility.
Flank~The files that do not belong to the centre, that is the a, b and c files on the queenside, and the f, g and h files on the kingside.
Flank attack~Attacking on either the kingside or queenside. 
Fluid pawn structure~ where future pawn movement is likely.
Focal point~A weak square near the enemy king. 
Fool's mate~The simplest Checkmate possible
Forced~A move or series of moves that must be played to avoid loss of the game or catastrophic loss of material.
Forcing move~A move which leads the opponent into a forced move or moves.
Forepost~An advanced square which cannot be attacked by a hostile piece of inferior rank.
Fork~A form of double attack where one piece threatens two enemy pieces at the same time. In a triple fork, three enemy pieces are threatened.
Fortress~A defensive blockade to keep out the enemy forces, especially the king.
Forward Pawn~A pawn that is at the very front of a pawn chain. It is the only pawn contained in the chain that does not protect another pawn.
Frontal assault~A direct attack on an enemy pawn that is located on the same half-open file as your heavy pieces.
Gambit~Where the first player voluntarily sacrifices a pawn or piece in the opening for positional or developmental advantage.
General principle~a basic rule that serve as guidelines for less advanced players.
Ghost~a threat created in the mind of inexperienced players due to lack of confidence or fear of their opponent.
Good bishop~A bishop not hindered by friendly pawns on the same colour squares.
Grab~to capture a piece, perhaps making a positional concession in the process.
Grandmaster~The highest title apart from World Champion that a chess player can achieve.
Grandmaster draw~A quick, uninteresting draw.
Half-open file~A file with pawns of only one colour on it.
Hanging~A pawn or piece subject to immediate capture.
Heavy piece~a Rook or Queen, also known as a "major piece" or "heavy artillery."
Hold~To hang on, to allow a successful defense.
Hole~A square that is undefendable by pawns. 
Illegal move~A move made contrary to the rules of chess.
Imbalance~A noticeable difference between the white and black armies.
Impossible move~A move which has obvious unfavourable results, and so is to be avoided.
Inactive piece~A piece not directly involved in the flow of the game.
Initiative~The player that is on the attack, or otherwise applying pressure to the opponent on the defensive, is said to "have the initiative."
Innovation~A novel move or idea in an established line of play.
Insufficient material~When neither player has enough pieces to mate their opponent.
Interference move~A move which obstructs the line of attack of an enemy piece.
International master~The next highest title below Grandmaster.
Interpose~the placement of a piece between an attacking enemy queen, rook or bishop, and the piece being attacked.
Intuition~An ability of an experienced player to decide on a move or plan by feel, rather than by extensive analysis.
Isolated pawn~A pawn with no friendly pawns on the adjacent files.
J'Adoube~ the expression used prior to a piece being adjusted on its square.
Kingside~The half of the board from which the king starts. The e, f, g and h files.
Knight on the rim~A knight on the edge of the board. 
Locked centre~Similar to a fixed centre except that no pawn movement is possible.
Luft~Moving a pawn so the king has an escape square to prevent back-rank mates.
Main line~The principal variation used or analysed.
Major piece~A rook or queen.
Manoeuvre~A series of quiet moves designed to redeploy your pieces more favourably.
Master~A player whose Elo rating is 2200 or higher.
Material~Your pieces and pawns, excluding the king.
Mating attack~An attack against the enemy king that leads to possible checkmate, or where mate can be averted by the enemy sacrificing material.
Mating net~A mating attack that leads to mate with correct play, no matter what the enemy does.
Middlegame~The phase of the game between the opening and endgame. 
Minor piece~A bishop or knight.
Minority attack~An attack on a pawn majority by a pawn minority. 
Mobility~How much freedom of movement the pieces have.
Notation~A system of symbols and coordinates for recording the moves of a game.
Occupation~ the placement of a rook or queen on a rank or file, or a bishop or queen on a diagonal, to exert control over it.
Open file~A file where no pawns are present.
Open game~A position where there are few centre pawns, and many open attacking lines.
An Opening~A specific sequence of moves which have been catalogued over time. 
Opening repertoire~A set of openings that a player prepares in advance to get to a preferred middlegame position.
Opposite colour bishops~Where each side has only one bishop that travels on squares of a different colour from that of the enemy. 
Opposition~An endgame term meaning the king not forced to move. 
Orientation~The way the board is positioned with a white square on a player's right hand corner.
Outflanking~A manoeuvre in the endgame with kings where one makes forward progress up the board.
Outpost~A safe square in enemy territory that is protected by friendly pawns or pieces, and can be occupation by one of your pieces.
Outside passed pawn~A passed pawn on the flank which is far from all the other pawns on the board.
Overextended~The position in which a player's position is left with various weaknesses and no compensation for them.
Overprotection~Defending a strong point more times than appears necessary. 
Overworked piece~A piece which is required to do too much, defending too many pieces or squares at once. 
Passed pawn~A pawn that has advanced past any enemy pawn that could hinder or capture it.
Passive~An inactive move or plan that doesn't fight for the initiative. 
Pawn centre~the pawns based in the centre of the board, primarily on d4, e4, d5 or e5.
Pawn chain~Two or more similarly-coloured pawns linked on a diagonal. 
Pawn contact~Opposing pawns are "in contact" when they are able to capture each other. 
Pawn duo~Two pawns of the same colour that are side by side and touching each other.
Pawn island~A group of pawns of the same colour separated from the next pawn by at least one open file.
Pawn storm~Advancing one or more pawns towards the enemy king with the intent of ripping up his pawn cover. 
Pawn structure~The position of all the pawns.
Petite combination~A combination involving only a few moves and often only one tactical theme.
Perpetual check~Unremitting attack on a king, without checkmate. Under some rules this may result in a draw.
Piece~Sometimes used in a particular sense to refer to any piece other than a pawn.
Pin~an at attack by a queen, rook or bishop on a piece which cannot move without exposing a more important piece or square.
Pinned piece~The piece under attack which cannot or should not be moved because of a pin.
Pinning piece~The attacking piece in a pin.
Plan~A short or long term goal which a player bases his moves on. 
Point count~A way of determining the worth of the pieces by assigning them a numerical value. 
Poisoned pawn~A pawn that, if captured, would cause serious disadvantage to the capturing side.
Position~The arrangement of the pieces on the board at any given moment.
Positional~A move, series of moves, plan, or playing style concerned with exploiting small advantages.
Positional mistake~A mistake which will lead to a disadvantage by surrendering critical squares time or space.
Positional sacrifice~A sacrifice that has no immediate tactical results, but will lead to a positional advantage.
Premature~A hasty move or series of moves or plan, or to act without enough preparation.
Prepared variation~A very well researched opening variation, often strengthened by new moves. 
Problem child~A blocked in queen bishop.
Prophylaxis~A strategy explored by Nimzovich, where you prevent your opponent from taking action in a certain area for fear of reprisal.
Promotion~When a pawn reaches the final rank, it can be turned into another piece, except a pawn or king, usually a queen. 
Protected passed pawn~A passed pawn that is protected by another friendly pawn.
Queenside~The half of the board from which the queen starts.
Quiet move~A move that neither captures anything, checks, or directly attacks an enemy piece.
Rank~A row of eight squares across the chessboard. 
Rating~A measure of a player's skill, calculated as a number using a generally accepted formula by an official organization.
Redeploy~To manoeuvre a piece onto a more effective square, file or diagonal.
Refutation~A move or series of moves that demonstrates a flaw in a game, move, plan, variation, or analysis.
Resign~When a player sees his position is hopeless, and ends the game before checkmate.
Restrain~Controlling the enemy pieces in order to keep them from becoming active.
Risk~A move or series of moves designed to gain an advantage but which has a chance of causing a disadvantage.
Romantic~An era when all players attacked and sacrificed. If a sacrifice was offered, it was considered cowardly not to take it.
Rook lift~Moving a rook off the bank rank, and up a few squares, in order to slide it to a new file so it can help in the attack.
Royal fork~A fork between king and queen.
Running~Rapidly transferring the king from one sector of the board to another in order to evade attack.
Sacrifice~Voluntarily offering material in exchange for a perceived favourable advantage other than the material.
Sans voir~Playing chess blindfolded.
Scope~The number of squares to which a piece can move.
Screened piece~The piece which is guarded from attack in a pin.
Sector~One of three areas of the board, being the queenside, the centre, and the kingside.
Semi-open game~A position that contains some open and closed qualities.
Sharp~Bold, aggressive moves or positions.
Shot~A strong move that was not expected.
Simplify~Exchanging pieces in order to reach a winning endgame, neutralize your enemy's attack, or clarify the position.
Simultaneous play~A player contesting a number of games against a number of players at the same time.
Skewer~A tactic where an enemy piece is attacked and forced to move, exposing another enemy piece behind it to capture.
Smothered mate~Checkmate by a knight, all squares adjacent to the king being blocked by its own pieces.
Sound~A safe, solid position, or a correct plan or move.
Space~The amount of area of the chess board controlled by each side.
Space count~A method of counting the squares controlled or attacked by each side's pieces.
Speculative~A risky or unclear move or plan.
Squeeze~Exploiting a bind by the gradual build-up of pressure upon the enemy's position.
Stalemate~A position is which the player who's turn it is to move has no legal move but is not in check. A drawn game.
Strategy~The formation and execution of an overall plan.
Study~A make believe position that highlights tactical themes.
Style~Preferring certain type of positions and moves.
Support point~A square that serves as a home for a pieces, usually a knight, because they can't be driven away from it by a pawn.
Swindle~A trick pulled from an inferior position.
Symmetry~Where both armies, or both sets of pawns, are identically placed on their respective sides of the board.
Tactic~Trap, threat, or plan based on the calculation of combinations or variations.
Tempo~A unit of time represented by a move. 
Tension~A position where pieces and/or pawns face off against each other without capturing.
Theory~Known and played variations and positions in any phase of the game.
Threat~A move or plan, that, if allowed, leads to immediate reduction of the enemy's position.
Three repeats rule~A game can be drawn when the same board layout occurs three times during a game.
Time control~Used to limit the length of a game. It is the time allotted to reach a certain number of moves.
Time pressure~When one or both players has used most of their allotted time, and must make moves with little or no thinking
Transition~Changing from one phase of the game into another; i.e. from the opening into the middlegame.
Transposition~Reaching an identical position from a different sequence of moves.
Trap~A hidden method of luring the opponent into making an error.
Unclear~An uncertain situation in which is it not apparent whether either side has an advantage.
Underpromotion~Promotion of a pawn to anything other than a queen.
Variation~A line of play that is an alternative to the moves actually played.
Static Value~ is the nominal value of a piece. 
Dynamic Value~ is the value of a piece in its current position, accounting for mobility, attacking strength, defending ability etc.
Valve~A move which simultaneously opens one line of play while closing another.
Weakness~A pawn or square that is difficult to defend.
Wild~Extremely unclear position or move, with almost unfathomable complications.
Zeitnot~time trouble.
Zugzwang~ A position where a player would prefer to pass his move as any move damages his game.
Zwischenzug~An unexpected move tossed into an expected series of moves.