The document discusses AVL trees, which are self-balancing binary search trees. It describes how AVL trees maintain a balance factor of -1, 0, or 1 to ensure a height balance during insertion and deletion. It explains the different types of rotations (single, double) needed to balance the tree when the balance factor is outside this range after an operation. It also provides examples of insertion, deletion, and the resulting rotations to maintain a balanced AVL tree.