A squeeze that is effective against one opponent but not the other, ie it will not operate if you interchange the opponents’ hands.
A common reason why a squeeze works against one opponent only is if both threats are in the same hand, which means they will need to lie over rather than under the stoppers.
For example:
Both threats are in the North hand, so when South leads the ♣A West is squeezed in the majors. If you swap the East-West cards, the squeeze would fail because East discards after North and would discard the same suit as North.