Call queue
A call queue is the holding pattern a phone system places incoming calls in when no one is available to answer. Calls are released in order, usually first in, first out, as agents become free.
Also called: hold queue, queueing, waiting queue
Queued callers typically hear music or announcements, sometimes an estimated wait or their position. The queue is managed by the ACD, which applies the routing rules and decides who answers next. Queues can have a maximum length or wait time, after which calls overflow elsewhere.
Queues exist because human capacity is fixed. They trade a missed call for a waiting one, and the length of that wait is what drives abandonment rate. A system with no concurrency limit has no queue in the traditional sense, since every call can be answered as it arrives.