Inorder traversal: The left sub tree is visited, then the node and then right sub-tree.

Algorithm for inorder traversal is following:

1. traverse left sub-tree
2. visit node
3. traverse right sub-tree

Figure: An expression tree: An inorder traversal

Inorder traversal can be best explained by an expression tree, where the operators are at parent node & operands are at leaf nodes.

Let us assume the above expression tree .The postorder , preorder, and inorder traversal are following:

preorder Traversal :  + * / 4 2 7 - 3 1

 postorder traversal :  4 2 / 7 * 3 1 - +

inorder traversal    :  - ((((4 / 2) * 7) + (3 - 1))

There is another tree traversal (certainly, not very common) is called level order, where all the nodes of the similar level are first travelled starting from the root .

Figure: Tree Traversal: Level Order