Here are some chess-related terms that you may found in tournaments:

'Blunder' : To totally miss something which is obvious, so that the opponent will now benefit.

'Patzer' : A player who can not improve his play, though he is playing for years. A patzer is blundering all the time.

'Trap' : A move that is trying to induce a mistake.

'Opening' : the first 10-15 moves of the game. It is the first phase of the game.

'Endgame', 'Ending' : The last of the three phases of the game, when only a few pieces are left on the board.

'Middlegame' : The second phase of the game. Most of the action is taking place in the middlegame.

'File' : a column in the chessboard.

'Rank' : a row in the chessboard.

'Wing', 'Side' : The board can be divided into two halves : the queen's wing or queenside (including files a-d) and the king's wing or kingside (including files e-h).

'Light piece' : A bishop or a knight.

'Heavy piece' : A queen or a rook.

'Light-squared bishop' : A bishop, either white or black, that moves on the white squares.

'Dark-squared bishop' : A bishop, either white or black, that moves on the black squares.

'Check' : To threat the opponent's king.

'Checkmate', 'Mate' : To threat the opponent's king, so that it he has no escape.

'Stalemate' : A player is stalemated if he has no valid moves at his disposal, but he also is not in check. The game is drawn in this case.

'Material' : One or more pieces, not including the king.

'Development' : The procedure of moving the pieces from their initial positions into more active squares. It is very important to develop one's pieces in the opening.

'Tempo' : The time to play a move. To 'win a tempo' means to proceed in such a way, that it is as if one was making two moves instead of one. This may happen, for example, when threatening the enemy Queen, whilst proceeding in development; the opponent will have to move the Queen and delay his own development by one tempo.

'Threat' : A move that practically forces the opponent to defend against, or he will lose something.

'Pin' : to make a move that prevents an enemy piece from moving, or if it does, another enemy piece behind it (lying in the same rank, file or diagonal) can be captured. The pin is an 'absolute pin' if the second piece is the King; in this case the pinned piece can not move at all.

'Exchange' : To capture an enemy piece and let the opponent capture a piece of the same value.

'Simplification' : One or more exchanges lead to simplification of the position.

'Sacrifice': A purposed loss of material in order to bring in (usually after a combination) a bigger advantage.

'Gambit' : A pawn sacrifice in order to achieve something, usually a valuable tempo or the opening of files, diagonals etc.

'Variation' : A possible sequence of moves that arises from a position.

'Combination' : A sequence of moves that results in an advantage, either material or positional.