In a way, they are.
Back ribs, also called baby back ribs, are the ribs on either side of the spine. The rest of the ribs that aren't back ribs are called spare ribs. Take as rack of spare ribs and cut away the breast bone and what are called rib tips so the remaining rack is basically rectangular, and you have what are called St. Louis cut ribs.
This is not to be confused with St. Louis style of cooking ribs, which is grilling the ribs instead of smoking them.