What principle underlies how a queue works?

The queue's operation is based on the FIFO (First In, First Out) principle: first in, first out.

This means:

• elements are added to the end of the queue,
• they are removed from the front,
• the processing order exactly matches the order of arrival.

Example: if you add 1, 2, 3 to a queue one after another, they come out in the same order when removed: 1, 2, 3.

In this way, a queue models the natural order of waiting: like a line of people at a checkout.