In video games, when the makers increase the power of something, it is sometimes referred to as a buff. If they decrease the power of something, it is called a nerf or a de-buff. This also applies to player abilities to temporarily increase or decrease their power.
Where do these terms come from?
Best Answer
Wikipedia gives info on origin and context of both terms:
You can read the linked articles for more.
Online Etymology Dictionary has an entry for buff as well: