Rib question..

Hello I know this has been asked before but I tried to search prior threads but here it goes...what is the main difference between spare ribs and baby back ribs? Is it just the way they are cut? I know when I grab a rack of ribs in the store and it says "baby back" on the package these are baby back. Are St Louis ribs considered spare ribs? Pork loin ribs considered spare ribs?  If the package does not say "baby back" are these considered spare ribs? How do I know when in the market when I pick up a pack of ribs if it is considered spare ribs or baby back(outside of the package saying baby back) Again hate to ask such a question, but I'm a new guy who is looking for all the knowledge he can get and this forum is super friendly and a easy place to ask such a basic question.  If one knows a prior thread that can help me understand the difference please add the link.

Thanks

-Rob