meaning of traversal
1.   traversal  Processing nodes in a graph one at a time, usually in some specified order.   Traversal of a tree is recursively defined to mean visiting the root node and traversing its children.   Visiting a node usually involves transforming it in some way or collecting data from it.  In "pre-order traversal", a node is visited _before_ its children.   In "post-order" traversal, a node is visited _after_ its children.   The more rarely used "in-order" traversal is generally applicable only to binary trees, and is where you visit first a nodes left child, then the node itself, and then its right child.  For the binary tree:      T     /     I   S   /   D   E A pre-order traversal visits the nodes in the order T I D E S.  A post-order traversal visits them in the order D E I S T.   An in-order traversal visits them in the order D I E T S. 
2.  travel across
						 
