Nerf is the term used to describe on the actions taken to a certain area from
people farming it so much, certain skills that are extremely overpowered,
or anything else in-between. Most people in the game, namely farmers and PvP
people get pissed when Arena Net starts to take the Nerf Bat to things in the
game.

Nerf got its original name from the toys, the Nerf toys. It’s like comparing
a Nerf Bat to a metallic bat, which one will hit softer? This is the same
thing as nerfing farming. When they nerf farming, they try to make less of
an impact on the rate of Gold Items and Runes drop.

EXAMPLE: It pisses me off that they haven’t nerfed IWAY builds yet.