The term “karat” refers to the percentage of gold versus the percentage of an alloy in a piece of jewelry or a decorative object. Gold is too soft to be usable in its purest form and has to be mixed with other metals. One karat is equal to one–24th part fine gold. Thus, 24 karat gold is 100 percent pure and 18 karat gold is 18/24 or 75 percent pure.