An isolated pawn is a pawn that cannot be protected by pawns of the same color -- that means there are no pawns of the same color on adjacent files. Isolated pawns can be a liability, if they can be attacked by the opponent. Since pawns cannot move backwards, the best solution is to attempt to exchange the pawn for an enemy pawn. If this is not possible, try to use captures to bring the pawn adjacent to another of the same color, or use a piece to protect it as a last resort. A pawn that is defended only by non-pawns (i.e. rooks, bishops, etc.) is a liability, because these pieces are tied down to the isolated pawn's defense and are generally unavailable for other purposes, because if they move the isolated pawn may be captured.