There are two different usages of the term; one refers to an ordered double-ended queue, the other to an improved heap.
The first version combines the properties of the double-ended queue (deque) and a priority queue and may be described as an ordered deque.
An item may be added to the head of the list if the new item is valued less than or equal to the current head or to the tail of the list if the new item is greater than or equal to the current tail.
The second version is a subject of patents[2][3] and improves the heap data structure.
The whole data pile based system can be generalized as shown: