Trillion or Trilliant: 

This cut was first developed in Amsterdam, although the design varied considerably based on the rough form of the stone. The year 1962 saw the Henry Meyer Diamond Company of New York design and trademark the modern Trillion cut and over time the trillion became the generic name for all triangular brilliant cut diamonds.

A triangular shape, comprised of three equal sides made up of 31 of 50 facets depending on whether the diamonds are used as solitaires or accent stones.

Solitaire stones are convex whereas accent stones are cut concave. Trillion cut diamonds are usually used as side stones to compliment larger solitaire stones in engagement rings although they also make for a perfect solitaire stone themselves considering their unparalleled brilliance and fire.