A queue data structure implements waiting in line: items are inserted ( enqueued) at the end of the queue and removed ( dequeued) from the front. Sometimes the term FIFO queue or just FIFO is used, for First-In First-Out.
A queue is a fair data structure: an entry in the queue will eventually be removed and get service. (A stack, in contrast, is unfair.)
Queues are frequently used in operating systems: