A passed pawn is a pawn for which there are no opposing pawns to prevent it from advancing to the eighth rank, i.e. no opposing pawns on a higher rank on the same file nor the files to either side. A passed pawn is sometimes called a passer. In this position, the white pawns on the b, c, and e files are passed pawns. Passed pawns are an advantage because it requires the intervention of an opponent´s piece to stop them from promoting. Often a piece must be sacrificed to prevent a passed pawn from promoting. The play of passed pawns is often of fundamental importance in endgames.
A pawn that is protected by its own pawns is called a protected passed pawn. In the first diagram, the b and e pawns are protected passed pawns. Two or more passed pawns on adjacent files are called connected passed pawns, and they are very strong. The b and c pawns are connected passed pawns. A pair of connected passed pawns is sometimes called a steamroller.
An outside passed pawn is a passed pawn that is one that is on the oppsite side of the board as the kings, e.g. the pawn on the a file in the second diagram. The black king will be diverted to stop White´s passed pawn and in the meantime, the white king can attack and capture black´s pawns, and win the game.