Let's familiarize ourselves with some terms we'll commonly come across in our upcoming discussion.
Here is a helpful diagram showing the terms:
A tree node's height is defined as the number of edges on the longest path to a leaf. A leaf node's height is 0. For example, in the preceding diagram, the height of the node h is 0.
The total number of children of a node is collectively referred to as the node's degree. A leaf node's degree is 0. In the preceding diagram, the degree of node a is 2.
A non-leaf node is also called an internal node. For example, in the preceding diagram, node c is an internal node, so are a, b, d, e, f, and g.
Every internal node in the preceding tree has the same degree: 2. This makes this tree a complete binary tree.
Refer to http://stackoverflow.com/questions/2603692/what-is-the-difference-between-tree-depth-and-height for more details and related discussion.