What does "cameo" mean?

Cameo: A carving in relief, esp. one on a small scale used as a jewel for personal adornment, or like. Note: Most cameos are carved in a material which has layers of different colors, such stones as the onyx and sardonyx, and various kinds of shells, being used. Cameo conch (Zoöl.), a large, marine, univalve shell, esp. Cassis cameo, C. rua, and allied species, used for cutting cameos. See Quern conch.