Item identifier

The item identifier is the globally unique (within IA) key used to identify and refer to a specific item (i.e. directory) of material. Only one instance of particular identifier can exist, and it will never change. There have been cases in the past where different identifiers that only differ in case of a letter or letters co-exist, although efforts are underway to prevent that in the future.

They are found in pretty much all URLs used to refer to items at IA, and most of the APIs.