The term CUT describes the quality of a diamond's proportions and symmetry.
These factors determine how much light a diamond captures and reflects. In other words, the level of brilliance of the diamond.
A perfectly cut diamond will reflect more light and appear visually larger than it actually is, as well as appear brighter and cleaner.
Therefore, it is important to pay attention to the angle at which the diamond reflects the light.
You can see in the image provided that a narrower or flatter diamond reflects less light. Poorly cut diamonds usually look worse than high quality cut diamonds.
Ideal/Excellent - Demonstrates optimal brilliance as it reflects virtually all the light captured by the diamond.
Very good - Adequately reflects most of the light. In normal lighting, the diamond is very similar to an ideal/excellent cut diamond, but its price is lower.
Good - Reflects some light and looks better than average. Excellent value for money.
Fair - Most of the light captured by a diamond escapes through the sides or bottom of the diamond, so the sparkle of the diamond is extremely low.
Poor - Most of the light comes through the sides or bottom, making the diamond look noticeably dull and lifeless. Such a diamond is worthless.