Two entirely different muscle groups used in different ways by the animal. That's what determines flavors in the meat (along with what hormones release in each muscle group, etc.) plus how much verigated fat (marbling), how much the muscle is used, what feed it's had, any fattening agents, sex, was it confined for fattening, and so on - tons of different factors.
History of the name and cut
American cuts of pork
It is said that in pre-revolutionary New England
and into the Revolutionary War
, some pork cuts (not those highly valued, or "high on the hog
," like loin and ham) were packed into casks or barrels (also known as "butts") for storage and shipment.
The way the hog shoulder was cut in the Boston
area became known in other regions as "Boston butt".