Post-order is a tree traversal method used in computer science, particularly with data structures like binary trees. In this approach, the nodes are visited in the following sequence: left subtree, right subtree, and then the root node. This means that the children of a node are processed before the node itself. This traversal method is useful for tasks such as deleting a tree or evaluating expressions in expression trees. By visiting the children first, it ensures that all necessary operations on the subtrees are completed before addressing the parent node.