While the first three criteria of 4C are dictated by the nature, cut is dictated by the hand of the man. The term “cuts” can make a reference as well to the shape of the stone (appearance of the diamond) as in the style of size (or arrangement of facets on the stone).
A well cut diamond can create spectacular lighting effects emphasizing three main characteristics:

Fires(Lights): the dispersal of the light through all the colors of the bright spectre
The shine: the total light reflected by the diamond
The sparkling: the brightness of light or the produced reflections when we move the diamond.

To understand well the cut of a diamond, it is necessary to begin by identifying its shape. There are indeed multiple possible forms, the most popular being the brilliant-cut diamond. Other forms of diamonds are called the “fancy” forms.