Term used to describe the fineness/purity of gold. A karat is one part out of 24 (this comes from ancient coins: At the time of Constantine, 24 kerations were equal to a golden solidus), so 24-Karat gold is completely pure. However, gold is so soft that 24-karat is not all that practical for jewelry, so 14-karat gold (14 parts gold, 10 parts some other metal) is perhaps the most common type used for jewelry.

Occasionally spelled "carat," but a carat is a unit used for the weight of gemstones, so the "k" spelling is much less confusing.