An ordered list in which all insertion take place at one end, the rear, while all deletions take place at the other end the front.

An ordered list in which all insertions and deletions are made an one end, called the top.

A finite set of nodes which is either empty or consists of a root and two disjoint binary trees called the left subtree and the right subtree.

A generalization of a queue because it allows insertions and deletions at both end.