How does a queue differ from a stack?

A queue and a stack differ in the order in which elements are processed:

• Stack: the LIFO (Last In, First Out) principle: last added, first out. Example: a stack of plates: you take the top one first.
• Queue: the FIFO (First In, First Out) principle: first added, first out. Example: a line in a store: whoever arrived earlier leaves earlier.

Technically:

• In a stack, additions and removals happen at one end (the top).
• In a queue, additions happen at the tail, removals at the head.

Summary: a stack keeps order "backward", a queue keeps order "forward".