Queue is an abstract data type or ordered collection of items where the addition of entities to the rear terminal position, known as enqueue, and removal of entities from the front terminal position, known as dequeue.
The most recently added item in the queue must wait at the end of the collection. The item that has been in the collection the longest is at the front. This ordering principle is sometimes called FIFO, first-in first-out. It is also known as "first-come first-served".