"Karat" and "carat" are two different terms used in different contexts:

1. Karat: "Karat" (often denoted as "K" or "kt") is a unit used to measure the purity of gold in jewelry. It indicates the proportion of pure gold in a piece of jewelry. For example, 24 karat gold is considered pure gold, while 18 karat gold contains 75% gold and 25% other metals like copper or silver.

2. Carat: "Carat" (often abbreviated as "ct") is a unit of weight used to measure gemstones, including diamonds. One carat is equivalent to 200 milligrams. The carat weight of a diamond affects its size and is one of the factors that determine its value.

In summary, "karat" refers to the purity of gold, while "carat" refers to the weight of gemstones like diamonds.