The History behind the Boston Butt (according to Wikipedia):
"Boston butt or pork butt is the American name for a cut of pork that comes from the upper part of the shoulder from the front leg and may contain the blade bone. Boston butt is the most common cut used for pulled pork, a staple of barbecue in the southern United States.
In Mexican Spanish, this cut is known as the espaldilla (literally "little back").