- Not available on that edition (the reason is in the tooltip)
- Depends on the setting, your class or another addon (details in the tooltip)
What it does
Checks if the unit specified has a debuff of the type you choose, such as Magic, Curse, Disease or Poison. With Dispellable ticked only debuffs the game says you can dispel count, and with Own Debuff ticked only debuffs you applied.
Why you might use it
Checks whether a unit has a debuff of a given type, such as Magic, Disease, Poison or Curse. Healers use it on a mouseover, target or focus to light up the matching dispel, such as Cleanse, Dispel Magic, Remove Curse, Cure Poison or Purify. Tick Dispellable to count only debuffs the game says you can dispel, though that does not check that your dispel is ready or in range. On Retail and WoW Forever the game can hide auras in combat, and the condition is then unavailable.
Example
your mouseover target has a debuff of type Magic that is dispellable
Settings
What each setting in the condition editor means, from the game's own help.
Unit - The unit this condition uses as the target of comparison.
Debuff Type - The type of debuff that is on Unit.
Own Debuff - Only consider auras that you applied yourself.
Dispellable - Only consider debuffs returned by the game's dispellable aura filter. This does not guarantee your dispel is ready or in range.