When we talk about queue we are really referring to a call queue. A queue can (but does necessarily) correspond to a specific department in your organization. In such a case when a caller chooses that department from the phone’s menu he will enter the queue.
A call queue's function is to place incoming calls in a line to be answered once an agent become available to answer them. The queued calls are distributed to the next available agent in the order received. After a queue has been created, it can be assigned certain greetings, messages, and hold music as well as triggers to determine what to do if the queue is too busy. Agents can belong to several queues and can log themselves in or out of queues.