A deque (short for "double-ended queue") is a data structure that allows insertion and deletion of elements from both the front and the back. This flexibility makes it useful for various applications, such as implementing queues, stacks, and even certain algorithms. Deques can be found in programming languages like Python and C++, where they are often part of the standard library. Deques can be implemented using arrays or linked lists, providing efficient operations for adding and removing elements. The average time complexity for these operations is O(1), making deques a performant choice for scenarios where quick access to both ends is required.