A binary tree is a rooted tree that is also an ordered tree (a.k.a. plane tree) in which every node has at most two children.
The height of a binary tree is the height of the root node in the whole binary tree.
Complete tree - is a binary tree in which every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible.
A balanced binary tree is a binary tree structure in which the left and right subtrees of every node differ in height by no more than 1.
A perfect binary tree is a binary tree in which all interior nodes have two children and all leaves have the same depth or same level.