This is the top portion of the shoulder from the backbone down to the top of the Picnic Shoulder, including the shoulder blade. It may be sold skin-on but is more commonly without skin and often without bone. If boneless it may be rolled up and secured with netting.
The term "butt" has nothing to do with the rear end of the pig, this is the front shoulder. Some say it was called "Boston Butt" because it was packed in a barrel called a "butt" but I think that's reaching.
More on Cuts of Pork.
Buying: This is one of the most common cuts of pork and can be found in any meat market that sells pork.
Cooking: The most common way for this cut to be cooked is oven roasted whole. The complex bone structure and significant internal fat deposits make other uses difficult.
Pork Shoulder Boston Butt Boneless - [#406A]
This is the boneless version of the Boston Butt, actually cut a bit different from the regular version. This cut is often rolled and secured with netting to provide a uniform roasting thickness.
Cooking: This cut will normally be oven roasted whole, but
it can be cut up for other uses.
Shoulder Blade Steak - [#1406]
This is the pig version of the beef "7 bone steak", a slice from the Boston Butt. A boneless version is #1407.
Cooking: This cut can be pan fried like pork chops, but
will have more flavor and be a little tougher.