Cut
How well a diamond's angles and proportions are shaped — the single biggest factor in how much it sparkles. Matters more than colour or clarity for visual impact.
Clarity
How free a diamond is from natural internal marks (inclusions) or surface marks (blemishes), graded from Flawless down to Included. Most SI1–SI2 inclusions are invisible without magnification.
Colour
Graded D (colourless) to Z (visibly warm), for white diamonds. Most people can't tell D from G without a side-by-side comparison.
Carat
A unit of weight (0.2 grams), not size — two diamonds of the same carat can look different sizes depending on shape and cut.
Certificate
An independent lab's report grading the diamond (GIA is the most widely trusted). Always ask for one on anything over about half a carat.