The Boston Butt is a cut of pork that barbequers often used for BBQ pulled pork.
This cut comes from the upper part of the front leg of the pig. Boston Butt is cut from the top part of the shoulder and may contain part of the shoulder blade.
People that smoke or barbeque the Boston Butt will debate whether bone-in or boneless is better. We think bone-in makes tastier pork but of course when buying by the pound you are paying for the bone.