What property makes a binary search tree useful and how do you validate one?

A binary search tree, or BST, maintains the invariant that every node in the left subtree has a value less than the current node, and every node in the right subtree has a value greater. This enables O of log n search, insertion, and deletion in balanced trees. To validate a BST, perform an inorder traversal and verify the values are in strictly ascending order, or recursively pass down valid ranges for each node. A common mistake is checking only the immediate children instead of the entire subtree.