A passer far from the main action decoys the enemy king away. While they chase, your king walks the other flank and eats. Worth about a pawn and a half: trade into endgames when you have one.
Remember
• Outside passer: a passed pawn far from the other pawns and the enemy king.
• The opponent's king must chase it: that's the decoy.
• Your king walks the other flank and eats the remaining pawns.
• Worth roughly a pawn and a half. Trade into endgames when you have one.