HEAP
A heap is described to be a binary tree with a key in every node, such that
1-All the leaves of the tree are on 2 adjacent levels.
2- All leaves on the lowest level happen to the left & all levels except possibly the lowest are filled.
3- The information the root is at least as large as the keys in its children (if any) & the left & right sub trees (if they exist) are again heap.