Tripe: muscle or organ?

Send Camas Davis of the Portland Meat Collective and see if she can tell you. I know it's from the first 3 chambers (rumen, reticulum, and omasum) of the stomach of cattle (maybe other ruminants as well), but I don't know if it's just the mucosal layer or if the muscularis layer is also included. My inclination would be to call it organ, but I bet Camas would know or be able to refer you to someone who does.

Technically it consists of slow muscle fibers, rather than the striated muscles that constitute meat. But these are so morphologically different!

It is both. It falls in the offal category, which anatomically speaking is distinct from the category of muscles and the category of bones. However, there are three different types of muscles in the human body - skeletal muscles, smooth muscle, and cardiac muscle. Tripe is of the smooth muscle variety whereas steak is of the skeletal muscle variety. Skeletal muscle has the filaments that you observe when you cut or pull meat, and smooth muscle has a different more unified structure because of the way it functions.

It's stomach lining, so wouldn't that make it a tissue? It gets lumped with organs, but it's definitely not a muscle.

I always thought it was both since the stomach is defined as a muscular organ.