There are two ways to measure vertical distance in a tree.
Depth: Distance from the root to a node.
The root has depth . Its children have depth . Their children have depth . And so on.
Height: Distance from a node to the deepest leaf below it.
Leaves have height . A node with only leaf children has height . The root usually has the maximum height. Depth goes down. Height goes up. They are inverses in a sense.