Negative Play Experience
From LOTR-TCG Wiki
Negative Play Experience (usually just shortened to NPE) is an informal term. NPE cards are obnoxious cards. That can be because they're overpowered, but usually it means they're obnoxious in some other way. If a hypothetical card wanted you to search your deck for every card where the third word is "the", that would be a NPE, because it would waste everyone's time while you check every card.
Unofficial formats often X-List or errata NPE cards. Fixing NPE cards is one of the main goals of the PC Errata project.
Along with being overpowered, being an NPE is one of the main ways a card can be broken.