Diamonds are often described in terms of the 4 C's

Colour
Diamonds vary in colour from yellow-brown to brilliant white. Each colour grade is assigned a letter grade with D being the highest white grade. Rare coloured diamonds are also available and are called fancies.

Clarity
The clarity of a diamond is how clear it is of flaws, (small cracks and bubbles). A code is assigned to describe the clarity. IF stands for internally flawless and is the highest clarity. VVS, VS and SI are progressively more flawed.

Cut
The cut of a diamond is the shape. This can be round, (brilliant cut), square, (princess cut), octagonal, (emerald cut), and many more. The quality of the cut affects the amount of light reflected back to the eye so a better cut diamond will sparkle more.

Carats
The size of a diamond is measured in carats. A carat is a unit of weight and is equal to one fifth of a gram. A one carat diamond measures around 6.5mm.

In addition to the 4C's there are several other characteristics a diamond may have. These are: Symmetry, Polish, Hearts and Arrows, Fluorescence and Certification.