Buff and nerf
Also said as Balance patch, Rework
A buff makes something stronger and a nerf makes it weaker. Nerf is named after the foam toys: a nerfed weapon is one that now hits like foam.
Balancing a live game is mostly making these changes in small steps, because small numbers move results a long way. A nerf also feels like having something taken away, so a buff to everything else is often the better-tasting fix.
Say it
“Nerf the shotgun's range by 10%, and leave its damage alone. Change one number per patch, so we can read what it did from the win rates.”
Where you’ve seen it
Ultima Online is where the word reached online games. Its designer Raph Koster has confirmed it, after players complained that a change had left their swords useless, though Merriam-Webster says the origin isn't certain.
Not to be confused with rework
A buff or a nerf changes a number. A rework changes what the thing does, usually because no number could fix it.