What cuts are "stir fry beef" and "stewing beef"?

They are not equivalent cuts and 'should not' be used interchangeably.

• Stir Fry meat is cut from the more tender cuts of beef (tri-tip, sirloin, rib-eye) and don't require much time cooking to be 'ready to eat'.
• Stew Beef is from less tender cuts (the Chuck or Eye of Round) which will become tender after a 'significant' time braising (cooking in liquid).

That said...the food police won't show up at your door if decide to interchange these, and using stir fry beef for stew isn't a terrible thing to do...but you will likely not be happy if you try to switch the other way.

I believe them to have interchangeable meaning, the small difference would be the size of the meat. You are going to see more consistency in size with stewing meat and the size is typically going to be a little thicker opposed to stir fry, which is just a fancy way of saying the trimming's. In regards to the cut: "stir fry beef" could be all cuts. "Stewing beef" is most likely going to be tougher less-expensive cuts, but in reality these two items are there to squeeze every penny out of the primal.

These are the two stages that are usually quickly made while cleaning cuts of meat. Next goes to the hamburger stage which is another topic in it of itself (stir fry vs. stewing vs. hamburger).