18k gold is a type of gold alloy that contains 75% pure gold by weight and 25% other metals, such as copper, silver, or zinc. Like 22k gold, the "k" refers to the karat measurement system used to indicate the purity of gold.

18k gold is commonly used in fine jewelry because it has a high gold content and a beautiful, warm color that is highly prized. It is also more durable than higher-purity gold alloys, making it a popular choice for engagement rings, wedding bands, and other pieces that are worn on a daily basis. However, because 18k gold is not completely pure, it may be more susceptible to tarnishing and may require occasional cleaning and maintenance.