All Purpose Flour is just what it says--you can get away with using it across several types of baking, if you only want to fool with one main type of flour. But it is no doubt the grain that is ground a standard amount (compared to cake flour is a finer texture or many "whole grains" that are coarser). No leavening added, and it is often "bleached" (when I find unbleached flour for a comparable price I buy it instead. My little store doesn't carry it, alas.)

I keep a container of white flour, and one of whole wheat. I don't bake cakes often so I don't keep that kind of flour here. And there are many others--you can grind all sorts of things into a powdery consistency.

This doesn't touch on what the additives are. . .

SRS