Ever wonder the difference between 18 karat gold and 14 karat gold? Here's a quick explanation to help clear things up. Gold is not a very strong metal, so alloys are usually added to help strengthen it.
A karat is a measure of the fineness of gold. 24 karat is pure gold. One karat equals 1/24 or 0.0417. Thus 14 karat gold is 14/24 pure gold and the balance (10/24) is alloy. The usual alloy metals are silver, copper, and zinc. Nickel is used in white gold.
Here's a quick chart for your reference.