Threaded binary tree: Consider the linked illustration of a binary tree 'T.  Approximately half of the entries is the pointer fields 'LEFT' and 'RIGHT' will have null elements. This space may be better used by replacing the null entries by some other type of information. Especially we will replace certain null entries by special pointers which points to nodes in the tree. These special pointers 4 are known as 'threads' and binary trees with such pointers are known as 'threaded trees'. There are two main types of threading: - one way threading and two way threading.