Battery:

Doubling Rooks on a file, or a Queen and bishop on a diagonal.

Bishop pair:

Two bishops are considered an advantage over a bishop and knight or two knights because they control diagonals of both colors.

Blockade:

To stop the advance of an enemy pawn by placing a piece directly in front of it.

Blunder:

A horrible move, usually resulting in the immediate or eventual loss of the game.

Doubled pawns:

Two pawns of the same color lined up on a file.  Considered a disadvantage because the pawns can no longer protect each other.

Draw:

A tied game.

Gambit:

A type of opening where at least a pawn is sacrificed in return for a compensating advantage.

Half-open file:

A file that contains none of one player's pawns, but at least one of his opponent's.

Hanging:

A piece or pawn that is unprotected and may be captured without capturing back.

Open file:

A file that is free from pawns.

Passed Pawn:

A pawn whose advance to the 8th rank can no longer be affected by any enemy pawn.

Protected Passed Pawn:

A passed pawn that is defended by another pawn.

Zugzwang:

Compulsion to move.  It refers to a situation where a player's position is worsened by any move the player makes.

Zwischenzug:

In-between move.  A surprise move that is inserted into a logical series of moves that changes the result of the sequence.  For example, a check inserted into a series of exchanges that won material.