The category of diamonds that have been cut to what some labs call ideal Proportions. Each lab has its own criteria for an ideal cut. A Diamond Grading Report from AGS might include a Cut Grade of Ideal. Other labs such as GIA-GTL use terms such as Excellent to indicate their best grade.
A common question arises as to whether such cuts are noticeably better in beauty, or Light Performance. This is totally up to the viewer’s eye, and personal preference.
See our question about Ideal Cuts in our FAQ.