http://www.amazingribs.com/recipes/porknography/pork_cuts.html
Pigs have 14 rib bones. They are attached to the spine and are usually divided into four popular cuts: Baby back ribs, spareribs, St. Louis cut ribs, and rib tips.
Starting at the top are the baby backs, closest to the backbone, nestled beneath the loin muscle. They are curved, round bones, close together, and most of the meat is on top of the bones, cut from the underside of loin muscle.
As you move further from the spine, the bones get larger, flatter, straighter, and wider apart with more meat between them. There is more fat marbling in the meat as you go further from the spine and closer to the belly. The front ribs are connected to the breast bone with a number of small bones and cartilage known as the rib tips. There are a number of other cuts, and they are all [described in the diagram on the right of the posted link, including country style].