A boule ring is a ring with a domed head which is usually set with pave set gemstones. It came in fashion around 1935. See also bombé.
The term boule (from French: ball, globe) is also applied to flame fusion synthetic gemstone rods (originally applied to the more globular shape of the first produced crystals).
1950's Gold and Diamond Boule Ring.
Photo Courtesy of Lang Antiques.