Souse is a variety of head cheese, usually specific to the Pennsylvania Dutch. They make their head cheese from the pickled meat of often otherwise unused animal parts (usually pork). These often include the feet, head, tongue, and heart.
The word itself probably comes from the Germanic souce, or pickling juice, which is related to sulza, or brine. Do you eat head cheese? We are always in favor of treating meat with respect, and this includes using the not-as-fashionable parts of the animal. Here's a recipe, just in case you are interested in making your own.
(Image credit: Karl Ehmer Deli)