A rib is part of a body found in the ribcage. In their plural form, ribs are also a culinary delicacy. (TXF: "Aubrey", "Red Museum")
In 1994, FBI Agents Fox Mulder and Dana Scully enjoyed eating ribs. Referring to a vegetarian cult in the area, Scully commented on the ribs by saying, "Ribs like these, I'd say the Church of the Red Museum has its work cut out for it." (TXF: "Red Museum")
The episode did not clarify whether the ribs were human or cow, although it is heavily implied that they are beef.