What is a heap and what are its types?

A heap is a complete binary tree that satisfies the heap property: in a max-heap, each parent is greater than or equal to its children, and in a min-heap, each parent is less than or equal to its children. Heaps provide O(1) access to the maximum/minimum element and O(log n) insertion and deletion. They are commonly implemented using arrays and are the basis for heap sort and priority queues.