The Princess cut is the square equivalent of the brilliant round cut, which normally comprises either 57 or 76 facets and a typical ratio of between 1.0 and 1.05.
It has a pyramidal shape with four beveled sides which creates more light dispersion than any other square shaped diamond. This makes it very popular for both solitaire engagement rings as well as earrings.
Since it is a patented cut, it can also be referred to as a Square Modified Brilliant on a laboratory certificate (i.e. GIA or AGS), or instead a Rectangular Modified Brilliant if it has a ratio greater than 1.05.
The “Princess Cut” name was originally used in connection with another diamond cut known as the “Profile” cut, designed by London cutter Arpad Nagy in 1961. The same name was later used and made popular by Ygal Perlman, Betzalel Ambar, and Israel Itzkowitz in Israel, who in 1979 created the Princess cut (also known as the Square Modified Brilliant) as it is known today.
There are other precursors of the Princess cut including the Barion (a square cut with rounded corners created in 1971 by South African cutter Basil Watermeyer), and the Quadrillion (a similar cut with only 49 facets, also created by Perlman, Ambar and Itzkowitz). After several years of optical research, the modern Princess cut was created, which is a square stone of 58 facets arranged similarly to those of a round brilliant cut diamond.