WoW API: GetInstanceInfo

Reference e
AddOns WoW API Widget API XML UI Event API WoW Lua Macro API CVars Battle.net HOWTOs Snippets UI tech Categories

Returns information about the current instances the player is in.

name, type, difficultyIndex, difficultyName, maxPlayers,
    dynamicDifficulty, isDynamic, instanceMapId = GetInstanceInfo()

Returns

name (string) - the name of the instance (localized), otherwise the continent name (eg: Eastern Kingdoms, Kalimdor, Northrend, Outland)
type (string) - "none" if the player is not in an instance, "party" if in party, "raid" if in a raid, "pvp" for battleground. Many of following result values will be nil or otherwise useless in the case of "none".
difficultyIndex (number) - the difficulty of the instance (see Details)
difficultyName (string) - the difficulty of the instance ("10 Player", "25 Player (Heroic)", etc)
maxPlayers (number) - maximum number of players permitted inside
dynamicDifficulty (number) - For dynamic instances: 0=Normal 1=Heroic
isDynamic (Boolean) - If the instance difficulty can be changed while zoned in
instanceMapID (number) - InstanceMapID for the instance. not the same as MapID.

difficultyIndex "difficulty level" is the difficulty mode like 10 / 25 player and described in GetInstanceDifficulty()
Is isDynamic is only useful in places like Icecrown Citadel where the difficulty mode can be changed on the fly.
mapID allows absolute identification of current instance without using localized names or other more complex means.

Added in 3.2, additional return values added in 3.3
In dynamic instances, difficultyIndex will only be 1 for 10man, or 2 25man.
In 5.0.4 dynamicDifficulty and difficultyIndex have changed. difficultyIndex is now used to determine a dynamic instance like heroic as well as 10 / 25 modes. dynamicDifficulty returns 0.
With 5.0.4 continents are considered 'instances', so when not inside an instance you are in a continent 'instance'.
mapID added in Patch 5.0.4