A queue in the everyday sense means to form a line and wait for attention.

This is not disimilar in a contact centre where calls are held in a queue until they are answered by available agents.

If there are no lines available the call treatment is 'engaged' or 'busy tone'.  If lines are available but there are no agents available the call will queue.

Queues can be either invisible or visible;

• Invisible Queue - where a caller in a queue is not aware of either their place in the queue or the expected wait time.  A caller in an invisible queue will become more frustrated as time passes.
• Visible Queue - where a caller will be aware of their position in the queue and/or the expected wait time. Here the caller can make an informed decision as to whether to hold.  They will give regard to the expected answer time and how quickly their position is moving in the queue.