Forced Move.—Is where the player has only one move at his disposal; for instance, in case of a check with a Knight, where the Knight cannot be taken, and the King has only one square to which he can move.
Fork.—This term is chiefly used where, by advancing a pawn, two pieces are attacked. (In Fig. 3, b, the white pawn forks K & B.) But it may also be used to express that any one piece attacks two others simultaneously.
Isolated Pawn.—Is a single pawn, the pawns of same colour on the right and left being off the board. A pawn is said to be "passed" when there is no pawn of the opposite colour which can bar its progress.
Gambit.[[76]]—Any opening in which a pawn is sacrificed by the first player in order to obtain a quicker development of his pieces is called a gambit. The pawn so sacrificed is called the "gambit-pawn." A counter-gambit is where the second player sacrifices a pawn with a similar object.
J'adoube.—("I adjust") is said by a player, to inform his opponent, before touching a piece or pawn of his own or his adversary's, that such piece or pawn is only to be adjusted, but not played.
Pin.—A piece is said to be "pinned" if it is attacked by an adverse piece in such manner that, by moving the attacked piece, a more valuable piece would be "unmasked," and left en prise; but chiefly if it is unable to move because it guards the King from being in check.
Value of the Pieces.
The approximate value of the pieces, as they stand on their respective squares at the beginning of a game, is estimated to be as follows: Taking the pawn as unit, the value of the Knight is 3.05; of the Bishop, 3.05; of the Rook, 5.48; and of the Queen, 9.94. German authorities estimate (taking also the pawn as unit), Bishop = 3; Knight = 3; Rook = 4½; and Queen = 9. The King in the End game is worth 4. Obviously the value of piece or pawn changes as the game advances, according to the position it occupies for the time being. There are, however, general principles which hold good in a large majority of cases. For instance, two Bishops are more serviceable than two Knights in the End game.[[77]] Bishop and Knight are also preferable to two Knights, but a single Knight is more serviceable, in most cases, in the End game than a single Bishop.