By changing the NULL lines in a binary tree to the special links called threads, it is possible to execute traversal, insertion and deletion without using either a stack or recursion.
In a right in threaded binary tree each NULL link is replaced by a particular link to the successor of that node under the inorder traversal called right threaded. Using right threads we shall find it easy to perform an inorder traversal of the tree, since we need to only follow either an ordinary link or a threaded to find the next node to visit.
If we replace each NULL left link by a particular link to the predecessor of the node known as left threaded under inorder traversal the tree is called as left in threaded binary tree. If both the left and right threads are present in tree then it is called as fully threaded binary tree for example: