Generic array of objects.
The Array object enables ArcObjects to pass around arrays of object references in a cross platform manner; you can store and retrieve an array of object references in the same way regardless of which ArcObjects API you are using. Unlike the similar Set object, Arrays offer random access by indexed lookup. You can also insert, remove, or replace objects at any position in the Array. The array is heterogeneous, that is the objects in it do not need to be of the same type.
Array objects are used by several interfaces including IIdentify and IMapControl2.