What grades of pork are sold in stores?

Excuse me, could you please elaborate on the various grades of pork that are typically available for purchase in supermarkets and retail stores? Are there specific standards or classifications used to differentiate these grades, and if so, what are the main factors that contribute to their designation? Additionally, could you provide some insight into the potential differences in quality, taste, and price among these various grades of pork, as well as any recommendations you might have for consumers when selecting pork products? Thank you in advance for your assistance.