There are three standard ways to visit all nodes: Preorder (root, left, right): Process the root first, then recursively process left subtree, then right subtree. Inorder (left, root, right): Process left subtree, then root, then right subtree. Postorder (left, right, root): Process both subtrees first, then the root.
The names describe when you process the root relative to its children. For a BST, inorder traversal visits nodes in sorted order. That's not a coincidence.
Inorder is "left before right," and in a BST, all left descendants are smaller than the root. Each traversal has uses. Preorder copies tree structure.
Inorder gives sorted order for BSTs. Postorder is natural for computing values that depend on children (like subtree sizes).