A queue is an ordered collection of items that follows the FIFO (First In First Out), also known as the first-come first-served principle. The addition of new elements in a queue is at the tail, and the removal is from the front. The newest element added to the queue must wait at the end of the queue.

The most popular example of a queue in real life is the typical line that we form from time to time:

We have lines for movies, the cafeteria, and a checkout line at a grocery store among other examples. The first person that is in the line is the first one that will be attended to.

A very popular example in Computer Science is the printing line. Let's say we need to print five documents. We open each document and click on the print button. Each document will be sent to the print line. The first document that we asked to be printed is going to be printed first and so on, until all the documents are printed.