This refers to the reflective qualities of a diamond. A good cut depends on the particular angles and finish that are used to give the diamond its brilliance.
A truly flawless diamond is very rare. Clarity is a measure of the flawlessness of a diamond and refers to the presence of identifying characteristics on (blemishes) and in (inclusions) the stone.
The colour of a diamond is a part of its composition and is an important measurement of its value. The less colour, the more value as a colourless diamond allows more light to pass through it and appears to reflect more sparkle.
Carat weight is a key measure of value. The larger the diamond, the greater the value per carat. But cut, colour and clarity also have to be taken into account when assessing the true value of a diamond.