Why is it that any graph traversal method can be described as pre-order, in-order, or post-order? What do those terms mean?

Question

There are several graph traversal algorithms in computer science ( vis. depth first, breadth first, etc. ). Furthermore, each of these algorithms can be implemented in pre-order, in-order, and post-order.

What do those terms mean? How do I properly categorize an algorithm as pre-order, in-order, or post-order?