A passed pawn is a pawn that has no opposing pawn in front of it on its own file or on either adjacent file, meaning no enemy pawn can block or capture it as it advances toward promotion.
It is one of the most important structural advantages in chess. A passed pawn creates a permanent, long-term threat: if it reaches the eighth rank, it promotes — most commonly to a queen. The further advanced the pawn, the greater the pressure it puts on the opponent. For instance, a white pawn on e6 with no black pawns on d7, e7, or f7 is a passed pawn threatening to promote in just two moves.
In practice, when you have a passed pawn, look to escort it with your king in the endgame, or support it with a rook placed behind it on the same file. Your opponent will be forced to commit pieces to stopping it, which often frees up space and activity for your other pieces elsewhere on the board.