A heap is a specialized tree-based data structure that satisfies the heap property, where the parent node is either greater than or equal to (in a max heap) or less than or equal to (in a min heap) its child nodes. This structure allows for efficient retrieval of the highest or lowest value, making heaps useful for implementing priority queues. Heaps are commonly implemented using arrays, where the parent-child relationships can be easily calculated using index positions. They are widely used in algorithms like Heap Sort and in managing resources in operating systems for scheduling tasks based on priority.