A Boston butt is the slightly wedge-shaped portion of the pork shoulder above the standard picnic cut[1] which includes the blade bone and the "lean butt" (which is boneless), both extensions of the tenderloin cut and can be used in place of the tenderloin.[2] Generally the pork shoulder is considered a primal cut with the picnic and butt sections being sub-primal cuts; however, some sources do refer to the butt as a primary cut.[3]
The tenderloin is closer to the rear of the hog. The shoulder is at the front.