In Australia, pototo starch and potato flour are the same thing: a very fine white powdery pure starch.
Actually, potato flour and starch are different things. The flour is made from the entire dehydrated potato whereas potato starch is made from the starch only. As I have never seen actual potato flour anywhere in Australia, when I say potato flour I actually mean the starch. Sorry to confuse anyone who actually has the two different types in their pantry.