What does nerfing mean?
Game balance
a change to a game that reduces the desirability or effectiveness of a particular game element
A nerf is a change to a game that reduces the desirability or effectiveness of a particular game element. The term is also used as a verb for the act of making such a change.[20] The first established use of the term was in Ultima Online, as a reference to the Nerf brand of toys whose bullets are soft and less likely to cause serious injury.[21][22]