In the gemstone world, a cabochon is a stone that is cut with a highly polished rounded or convex top with no faceting and a flat or slightly domed base. A cabochon may be cut in any shape, though oval is by far the most common.The term comes from the French caboche, meaning knob or small dome.n the gemstone world, a cabochon is a stone that is cut with a highly polished rounded or convex top with no faceting and a flat or slightly domed base. A cabochon may be cut in any shape, though oval is by far the most common. The term comes from the French caboche, meaning knob or small dome.