Pork Chops are simply slices across the loin. They fall into roughly three categories as shown in the photo. To the left is a chop near the shoulder end (#1410B), to the right a chop near the sirloin end (also #1410B), and in the center is the classic porkchop shaped center chop (#1412). Pork chops typically weigh between 6 and 8 ounces.
There are variations on the #1412L #1412A (Chine bone off), #1412B (boneless) and #1412E (boneless, single muscle and trimmed of nearly all fat). You aren't likely to see any of these variations in your local market - they're ordered by the restaurant trade.
More on Cuts of Pork.
Buying: If you want to serve pork chops, buy them already cut from the loin. The bones are too wide for simply cutting between them. Buy the cuts that are most suitable for your use.
Cooking: Pork chops are the primary pork cut for pan frying.
Some books on Asian cuisine recommend removing the bones and fat from pork chops and using the meat for stir frying. The reasoning is that loin meat is tender, and pork chops are an easily available form. Personally I don't give loin that much preference, other cuts have more flavor and just aren't tougher enough to worry about.