What is "queue"

Queues are structures based on the principle FIFO (first in, first out), where the elements that were inserted at the beginning are the first to be removed.

A queue has two basic functions: ENQUEUE, adding an element to the end of the queue, and DEQUEUE, that removes the element at the beginning of the queue. The operation DEQUEUE can only be applied if the queue is not empty, causing an empty queue error if this operation is performed in this situation.

Source: Wikipedia