What does it mean if an element of a video game has been "nerfed"?

When a video game has a feature that is more powerful or more of a game changer than the developers intended they may tweak it and make it less powerful. This process of weakening an ability is called being nerfed which is often very unpopular with players who have taken advantage of the "broken" part of the game. This is particularly the case when a gamer is playing a multi-user online game.

https://tvtropes.org/pmwiki/pmwiki.php/Main/Nerf