The World of Warcraft API uses rather complex values for some arguments and return values. Rather than re-explain them every time they're used, we document them as distinct data types (though in reality they're numbers and strings).
Complex World of Warcraft API Data Types
- actionSlot - Action button slot numbers (120 in total)
- auctionSortId - An identifier for sorting columns in the auction house.
- auctionTypeId - An identifier specifying which type of auction to operate on.
- bagId - Numbers representing bags you carry, bank bags, bank window, etc
- bagType - A bittype identifier representing the type of bags an item can go into or the type of items a bag can carry (New in 2.4.0)
- chatTypeId - An identifier for the different chat destination types.
- classId - An identifier for character classes.
- emoteToken - System names of voice/action emotes
- enchantString - An enchant id.
- enchantLink - A string that will be clickable, if shown in-game, contains an enchantString.
- fileID - A unique identifier for a client-accessible internal file (such as textures or models).
- GUID - A unique identifier for everything that can be interacted with.
- inventorySlotName - Names of inventory slots.
- inventorySlotId - Current mappings of slot names to numbers. May change.
- itemEquipLoc - String representation of where an item may be equipped ("INVTYPE_HEAD", etc)
- itemString - An item id with data about enchants, "of" type bonuses, and the item's creator.
- itemLink - A string that will be clickable if shown in-game, contains an itemString.
- itemType - String classification of an item, ("Armor", "Consumable", etc)
- lootMethod - An identifier for the different looting methods (group loot, need before greed, etc)
- mapID - A numeric identifier for a world/zone map.
- playerName - The name of a player.
- questID - A unique numeric identifier for quests.
- questLink - A string that will be clickable, if shown in-game, contains a questString.
- questString - A quest id with data about the quest, including the level and quest title.
- raidIndex - A number between 1 and 40
- standingId - Numeric encoding of faction standing.
- unitId - An identifier which specifies one of the units the API may reference ("target", "party1", etc)
- unitFlag - A bittype indentifier for the relationship between the player and a unit in the combat log (New in 2.4.0)
- difficultyIndex - A numeric identifier for dungeon and raid difficulty.
Category:API types has the full list. (Though if something there is not available here: please list it!)