- 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 one you can attack.
Why you might use it
Checks whether you can attack a unit, so damage steps only light up on something you are able to hit, not a friendly player, a neutral that will not fight, or a corpse. It is useful for hybrid healers who alternate between friendly and hostile targets, such as a Discipline Priest or a Restoration Shaman, and for mouseover or focus steps. See also Hostile and Is Friendly.
Example
your target is attackable
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.