The term integration stream tends to be used in at least two different meanings, usually defined by the context.
First of all an integration stream is a stream that is the stem, or the highest level within a UCM project. a UCM project always have exactly one integration stream, and as a project's integration stream, the stream actually have has certain properties and abilities compared to other (development) streams.
So in one layer of abstraction you can claim that there exist only two classes of streams: integration streams (belonging to a project) and all those that are not integration streams, typically refered to as just Development streams.
The second quite common use of the term integration stream is simply in the meaning "the stream I'm integrating or delivering into" which may not necessarily be a project's integration stream, it could easily be a team stream - which turns out to be just a variant of a development stream.
This sounds more confusing than it actually is because within the context the term is used it's often quite obvious (or not important) which meaning is used. If you want to be precise you can use the terms: "A project's integration stream" and "A development stream used for integration" to differ the two.