"Pork butt" is a cut of meat from the upper part of the shoulder. It is also known as "Boston butt" in the US, or "pork shoulder on the bone" in the UK. It is the cut of meat traditionally used to make the (Mexican?) dish carnitas.
See Boston butt, where it is actually marked as "blade shoulder".
However it is not easy to find it in normal supermarkets where I live, and I saw a suggestion online that I might find it more easily in Hispanic bodegas.
So what would you call this cut of meat in Spanish? (And most likely with a Mexican slant.)