Guild Wars 2

Does it mean to weaken?

Yep, that’s pretty much it. Sometimes skills are nerfed to prevent certain builds from being over-powered. Most recently, elementalists received a nerf because their bunker builds made them so hard to kill, it wasn’t really fair to anyone else.

Naturally, some people hate nerfs and some people ask for them.

http://en.wikipedia.org/wiki/Nerf_

Basically its an old old term came about when people started comparing changes to say a weapon getting its damage toned down to it being replaced by a nerf bat (soft foam weapons ftw)

Thanks for the answers.