What is "isolated pawn"

n. (context chess English) A pawn that has no friendly pawn on an adjacent file.

In chess, an isolated pawn is a pawn which has no friendly pawn on an adjacent file. An isolated queen's pawn is often called an isolani. Isolated pawns are usually a weakness because they cannot be protected by other pawns. However, there can be compensation, such as improved development and associated opportunities for counterplay, that offset or even outweigh the weaknesses associated with the pawn's isolation.

Many "textbook" openings lead to isolated pawns, such as the French Defence, Nimzo-Indian Defence, Caro-Kann and Queens Gambit.