The no. of children a node has is called its degree. The level of root is 0 & the level of any node is one more than its father. In the strictly binary tree shown above A is at level 0, B & C at level 1, D & E at level 2 & F & g at level 3.

The depth of a binary tree is the length of the longest path from the root to any leaf. In the above tree, depth is 3.

The other topics that will be covered regarding binary tree are listed below.
Representation of binary tree
Operations on a binary tree
Traversal of a binary tree