What is "passed pawn"

n. (context chess English) A pawn that has passed beyond enemy pawns on its own or adjacent files, and that hence has a clear run to the eighth rank.

In chess, a passed pawn is a pawn with no opposing pawns to prevent it from advancing to the eighth rank; i.e. there are no opposing pawns in front of it on the same file nor on an adjacent file. A passed pawn is sometimes colloquially called a passer. Passed pawns can be an advantage because only the opponent's pieces can prevent them from promoting.

In the diagram at right, the white pawns on b5, c4, and e5 are passed pawns. Black's pawn on d4 is a passed pawn. If Black plays fxg4, then Black will also have a passed pawn on g4, and White will have a passed pawn on f4.