The best way to differentiate between these is to look at the animal and see where they come from:

This is a whole pig with the backbone split down the center, but not separated. 

Let's split it:

Now, let's draw cut lines to separate out the parts'n'pieces:

and label them:

First, let's take the Pork Belly Spare Ribs: these also have the pork belly attached, so we have to separate them into:

Pork Belly:

and Pork Spareribs:(front and back views):

Now, from the whole sparerib comes the St. Louis Style sparerib:

where the Rib Tips are separated from the ribs, and the

skirt is removed from the rack along with the membrane:

The Finished St. Louis Style Ribs:

Then, there is the Carolina Sparerib:

with only the brisket section removed, giving easier carving into individual ribs.

Now, above the sparerib/belly section is the Loin:

If you bone out the loin, you end up with a boneless pork loin:

with the bones separated.

Cut the rib bones from the back bone:

And that is where baby back spareribs come from!

How much meat is left on from the loin is the choice of the meat cutter.