- 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 you, or the unit specified, are in a party or raid. With Raid ticked, only raid membership counts.
Why you might use it
Check whether you, or another unit, are in a party or raid. As a switch condition it picks a solo leveling rotation over a group one, and in a step it can limit group-wide buffs such as Arcane Brilliance or Prayer of Fortitude to when you are grouped. With Raid checked only raid membership counts, and unchecked a party or a raid matches; the Spell recipient unit only exists for announcements and is unavailable anywhere else. See also Instance and Class In Group.
Example
you are in a raid
Settings
What each setting in the condition editor means, from the game's own help.
Choose the unit whose membership in your party or raid is checked. Player keeps the original player group-status behavior. Spell recipient uses only the current announcement event context; without that readable context the result is unavailable. It never substitutes your selected target or a previous cast.
Checked tests raid membership only. Unchecked tests party membership or raid membership. A known nonmember is false; unavailable native data stays unavailable, including under NOT.