“Cameo (carving), method of carving, or an item (such as jewelry) made with the cameo method. The originator of the term.”(Wikepedia) Often seen in Ancient and Renaissance times. Cameo’s came from Semi-Precious stones such as multiple types of Onyx and Agate. The less expensive versions where made of Shell and glass. Typically worn as jewelry Cameos were most used for Signet rings.
Ive included some pictures below of Cameos that can be seen from the Art Institute of Chicago and wikepedia.com.