I am looking for a definition of a Queue in the Cisco environment.
In IPCC enterprise the queue is a logical concept. It's not like an ACD queue at all.
Think of it this way. If a call comes in on an Avaya which requests an adjunct route (host based route) and you don't answer this immediately but wait, you could order the requests and responses and produce your own queue. Do you have an ACD queue? - no.
When a call is queued in IPCC, the call is parked somewhere (IP IVR, CVP) and the Router is looking for the best target. The call is not queued in ICM.