Deque
In plain terms
A double-ended queue allowing inserts and removals at both ends.
Going deeper
A deque supports adding and removing from front and back efficiently, generalizing stacks and queues. It's useful for sliding-window and scheduling problems.
Under the hood
Typically O(1) at both ends via a doubly-linked list or circular buffer; backs sliding-window maximum and work-stealing schedulers.
Examples
Sliding-window algorithms, Python collections.deque, work-stealing queues.
Think of it like...
Like a hallway people can enter or leave from either end.