Backward Pawn

A backward pawn lags behind the pawns on its neighbouring files and can't advance to join them — an enemy pawn covers the square in front, and no friendly pawn can support its push. On a half-open file it becomes a fixed target the opponent piles rooks and queen onto. Unlike an isolated pawn it still has neighbours; it just trails them.

Source for further study: Soltis, Pawn Structure Chess.