Buff

Buff is a slang term for a spell that improves or protects a character. For example, casting enhancing spells likes Bull's Strength or Spell Resistance is called "buffing."

Buff can also refer to module creator changing the rules to enhance something. For example, changing the spell Bull's Strength to give 2d6 ability points instead of 1d4+1 might be referred to as "buffing" it -- the opposite of nerf.