- 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 classification of the unit specified, such as Elite, Rare or World Boss, is the one you choose.
Why you might use it
Checks a unit's classification: World Boss, Rare Elite, Elite, Rare, Normal, Trivial or Minus. Use it to spend long cooldowns and long damage over time effects only on bosses and elites, and to skip them on trash that dies quickly. It also works as a switch condition between boss and trash rotations. See also Level and Boss Mod Encounter.
Example
your target's classification is World Boss
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.
Unit Classification - The classification of Unit. This can be used to create conditions that only apply to certain unit classifications (eg. bosses).