The height of a binary search tree is the length of the ________ path from the root to a leaf.

The height of a binary search tree is the length of the longest path from the root to a leaf. In other words, it is defined as the number of edges on the longest downward path from the root node to a leaf node. The root of the tree is considered as level 0, and as you move down each level to the leaves, the height increases. If a binary search tree has more nodes, it usually indicates a greater height, which can affect the efficiency of operations like search, insert, and delete. A balanced binary search tree has a height of $O(\log n)$, which is optimal for performance. In contrast, if the tree becomes unbalanced, its height can become $O(n)$, leading to inefficient operations.