Lip-on?

What does it mean when the grocery ads say that a cut of meat is “lip-on” or “lip-off”? I’ve searched the internet, and I only find links to other grocery ads; no one seems to define it.

“Lip” means fat. The only cut I’ve seen this term used with is rib-eye, which is sold with the fat trimmed (lip-off) or not (lip-on). Many people think they’re saving money by trimming the fat themselves, but often they’re not.