Pawn Promotion
In chess, promotion is the replacement of a pawn with a new piece. It occurs immediately when the pawn moves to its last rank. The player chooses the new piece to be a queen, rook, bishop, or knight of the pawn's color. The new piece does not have to be a previously captured piece. Promotion is mandatory; the pawn cannot remain as a pawn.
Promotion to a queen is known as queening; promotion to any other piece is known as underpromotion. Promotion is almost always to a queen, as it is the most powerful piece. Underpromotion may be done for various reasons, such as to avoid stalemate or due to the knight's unique movement pattern. Promotion or the threat of it often decides the result in an endgame.