From Final Fantasy Wiki

Debuff is a term for spells and effects that grant status ailments or lower enemy ability scores or attributes. Generally these can be spells like Blind, which lowers enemy accuracy, or Gravity, or lowers enemy evasion, rather than spells like Fire which is a direct damage spell or Poison or Foe Requiem which is simply damage over time. In Final Fantasy XI, magic like this is found mostly in the category of Enfeebling Magic.

From GuildWiki

A debuff is some condition or hex which reduces a player's effectiveness. Examples of typical debuffs are health degeneration or energy degeneration, blindness and snares.

As a verb, "to debuff" means to use a debuff on a target.

Related articles

• Buff
• Condition
• Hex

From City of Heroes Wiki

Definition

1. A disadvantageous effect. For example, Envenom is a foe debuff.
2. The action of placing a disadvantageous effect on one or more foes. An example of debuffing would be the act of casting Snow Storm on an enemy.

The opposite of debuff is Buff.