Cut refers to two things. The first is the shape of the diamond, which can be round, marquise, pear, oval, princess, emerald, oval, heart or trillion.
Many people think fancy shaped diamonds cost more.
In most cases, however, it is exactly the opposite. The next aspect of cut is the quality of proportions . Cut, more than any other quality aspect, gives the diamond its sparkle. A diamond gets its brilliance and scintillation by cutting and polishing the diamond facets to allow the maximum amount of light that enters through its top to be reflected and dispersed back. When all the angles are correct, the light that enters is dispersed back through the diamond's top facets.