- 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 dead or a ghost. A unit that does not exist makes the condition unavailable rather than false.
Why you might use it
Matches when a unit is dead or a ghost. Use it for resurrection steps, such as Rebirth, Raise Ally or an out-of-combat Resurrection on a dead friendly mouseover or target, and under NOT to keep damage and healing steps from pointing at a corpse. A unit that does not exist, or cannot be read, makes the condition unavailable rather than false. See also Attackable.
Example
your mouseover target is dead or a ghost
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.
Matches when the selected unit is dead or a ghost. A missing or unreadable unit is unavailable, including under NOT. In a Via Macro announcement, choose Announcement target to follow the supplied unit.