- 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 is an enemy of yours, as the game reports it.
Why you might use it
Check that a unit is hostile to you before suggesting an attack on it, or that it is not before suggesting a heal or buff. It is handy for spells that work both ways, such as a Paladin's Holy Shock (damage on an enemy, a heal on a friend), and for mouseover rotations that should only offer damage spells on hostile mouseover targets. Works on every edition, and the game never hides it. See also Is Friendly and Attackable.
Example
your target is an enemy
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.