Definitions
1.VerbTo bump lightly, whether accidentally or purposefully."A racer will often nerf another as a psychological tactic."
2.VerbTo change a mechanic, an ability, or a character in a video game in order to make less efficacious."The lightning spell was originally pretty powerful, but in the sequel they nerfed it so it became completely useless."
3.VerbTo arbitrarily limit or reduce the capability of.
4.NounThe deterioration, weakening or worsening of a character, a weapon, a spell, etc.