- 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 kind of instance you are in, such as a dungeon, raid, battleground, arena or scenario, is the one you choose, and optionally its difficulty and which instance it is. Everything you set must match. Choosing Outside checks that you are not in any instance.
Why you might use it
Choose a rotation by the kind of place you are in: outside any instance, a battleground, an arena, a dungeon, a raid or a scenario. For example, switch to a PvP rotation with more crowd control in battlegrounds and arenas, or to an area-of-effect rotation in dungeons. Add an Instance Difficulty (its ID, blank for any) to separate, say, Heroic from Mythic, and an Instance ID to match one particular instance; the ID does not change with the game's language the way a zone name does. With no kind chosen, a difficulty or an ID alone decides. It can only be used in switch conditions, not in rotation steps. Outside only means not in an instance; see Outdoors for being outdoors and Zone for specific places.
Example
your instance type is Raid
Settings
What each setting in the condition editor means, from the game's own help.
Mode - The type of instance you are in.
Outside - You are not in an instance (this does not necessarily mean you are outdoors, just not in any kind of instance.)
Battleground - You are in a battleground (an ad-hoc instance where the opponent is the opposing faction.)
Arena - A close quarters fight with the opposing faction, where death is a loss.
Dungeon - A five-person dungeon, where your opponents are all NPCs.
Raid - An instance that accommodates more than five people, where your opponents are all NPCs.
Scenario - A single-person instance, similar to a dungeon but completed solo.
Instance Difficulty and Instance ID are optional. Every part you set must match, for example a Dungeon on Heroic difficulty, or one particular instance by its ID (the editor shows the ID of the instance you are in). The ID does not change with the game's language the way a zone name does.