Four C's of Diamond

Cut

Of all the 4Cs, diamond cut has the greatest effect on a diamond’s beauty. In determining the quality of the cut, the diamond grader evaluates the cutter’s skill in the fashioning of the diamond. The more precise the diamond is cut, the more captivating the diamond is to the eye. A facet is a flat surface on the geometric shape of the diamond. ... Some round brilliant cut diamonds have 58 facets depending on whether the culet is included. The facets are arranged in such a way to make sure the right amount of light enters the diamond, as well as reflect from the diamond.

Clarity

Flawless (FL) No inclusions and no blemishes visible under 10x magnification
Internally Flawless (IF) No inclusions visible under 10x magnification
Very, Very Slightly Included (VVS1 and VVS2) Inclusions so slight they are difficult for a skilled grader to see under 10x magnification
Very Slightly Included (VS1 and VS2) Inclusions are observed with effort under 10x magnification, but can be characterized as minor
Slightly Included (SI1 and SI2) Inclusions are noticeable under 10x magnification
Included (I1, I2, and I3) Inclusions are obvious under 10x magnification which may affect transparency and brilliance.

Color

Colorless (D,E,F) Highest-quality color grade a diamond can receive. A D-color diamond is extremely rare and emits unrivaled brilliance. Containing very minute traces of color, an E or F-color rated diamond emits a high level of brilliance and sparkle.

Near Colorless (G,H,I,J) Containing noticeable color only when compared to higher color grades, G or H color diamonds provide an excellent value. Whereas an I or J-color diamond typically appears colorless to the untrained eye yet contains slightly detectable color.

Faint Yellow (K,L,M) Faint color is noticeable. Even with the presence of color, these grades of diamonds can emit fire and beauty. Consider selecting a lower color when setting in yellow gold as color will be not as apparent.

Carat

Carat is the unit of measurement for the physical weight of diamonds. One carat equals 0.200 grams or 1/5 gram and is subdivided into 100 points.
Diamond price increases with diamond carat weight because larger diamonds are rarer and more desirable. However, two diamonds of equal carat weight can have very different values (and prices) depending on three other factors of the diamond 4Cs: Color, Clarity, and Cut