Diamond symmetry is graded using what appear to be vague adjectives but are in fact precise qualitiy tags:

Ex = Excellent, ID = Ideal [Different terms use by different labs. they are the same quality]
VG = Very Good
G = Good
F = Fair
P = Poor

A symmetry that maximizes the optimal light return is known as Excellent or Ideal, illustrated as perfect below. Diamonds with Premium and Very Good symmetry are well cut diamonds and have an abundant sparkle and presence. Good symmetry represents value for money but will not capture all the potential light return but will have a nice sparkle. Fair and Poor cuts should be avoided as they may be too shallow or deep and have a less than satisfactory performance.