Passed pawn
A passed pawn is a pawn with no enemy pawn in front of it or on an adjacent file, so nothing can step in its way.
Enemy pieces can still block or capture it, but no pawn can. That is why passers grow stronger as pieces come off: the king and a rook have to babysit a square that a pawn would have covered for free.
The pawn on d5 has a clear road. Black’s only pawn is on f7, two files away. White’s job is to escort d5; Black’s job is to blockade it, ideally with the king or a knight.
Creating a passer — by trading the last enemy pawn on neighboring files — is a common winning plan the coach will name in the endgame.