That’s a rather strange word to use in the context of beef, because they don’t really have anything resembling human lips. Which part of this, exactly, would you consider “lips”?
I think mouth, or perhaps snout, is a more accurate description here. Anyways, that’s the picture I found on Wikipedia when I looked for more information on where this meat might come from. Apparently it can also include the inner parts of the mouth, however, not the tongue, that’s considered a separate cut.