What does karat weight mean in metals?

Almost all gold used in jewelry is not 100% pure. This is because 24k gold is incredibly soft and too fragile to hold up long term. To make the metal more durable, gold is mixed with an alloy and Karats are used to measure the amount of pure gold used out of 24 parts. This makes it simpler to tell a metals composition at a glance. For example, if a piece is stamped 18k gold, it is understood to be 18/24 parts gold. This also means that anything 24k is raw gold.