Fortunately, I think there is a good empirical solution to your question, since I am not sure if my descriptive powers are up to the task of explaining "foamy" except to say...well, the egg whites get foamy. Anyhow, they reach this stage BEFORE they get to soft peaks, stiff peaks, or dry.

Anyway, if you are really going to be baking commercially, here is my suggestion: take some egg whites, and purely as an experiment, beat them gradually for a long time. Watch the stages they go through and make notes. If memory serves (and I am not sitting here beating egg whites as I write, so I may be screwing up!) they go from clear and jelly-like to slightly bubbly to having rather small bubbles (I'd call that the foamy stage) to getting white and making soft peaks to making stiff peaks to dry. If you add a bit of sugar, I think the progression is similar but the egg whites have a glossier look when they get white.

Experimentation with food is often too expensive and wasteful(that's why we all write asking each other questions, instead of just doing trial and error ourselves) but this one is probably an easy and worthwhile experiment that will help you with a lot of baking recipes. Good luck!