The light that is reflected off a diamond is known as the brilliance, and a well-cut diamond reflects almost all the light that enters it. Terms like cut and shape, however, are used interchangeably when talking about diamonds. "For us at James Allen, more than half the stones we sell are rounds," Dean said. "It's classic. It's traditional. And scientifically speaking, has the maximum brilliance because of the less light dispersion through the bottom of the stone. So I love round stones." For brides who are looking for something outside of a round-cut diamond, there are other options such as heart, emerald, and oval. Use the handy guide here to choose your favorite cut.