A backward pawn is one that has fallen behind the pawns beside it and can’t safely advance, leaving it stuck — often on a half-open file where it becomes a target.
Its neighbouring pawns have moved on, so no pawn can defend it from behind, and the square in front is controlled by the enemy — push it and it’s simply captured. So it sits there, defended only by pieces.
The real problem is the half-open file in front of it: the opponent stacks rooks and the queen on that file and piles pressure on a pawn that can’t run. Tying your pieces to its defence drains your whole position.
Backward pawns are a long-term weakness you provoke on purpose against the opponent — and avoid creating in your own camp. The square in front of it often becomes a lovely outpost for an enemy knight.
An isolated pawn has no friendly pawns on either neighbouring file. A backward pawn still has a neighbour, but that neighbour has advanced past it, so it can’t be defended by a pawn and can’t safely move up.
Because it usually sits on a half-open file where enemy rooks and the queen can attack it, and it can’t advance out of trouble — so you’re forced to defend it with pieces.
BetterChess is a practice tool — we make no guarantee you'll reach 1800 or any rating. Definitions are standard chess terminology; every diagram position is checked legal with the same engine the board runs.