What does au mean on a au10k necklace?

The "au" on a 10k necklace indicates that the piece is made of gold, as "Au" is the chemical symbol for gold on the Periodic Table. The "10k" signifies that the gold content is 10 karats, meaning it contains 41.7% pure gold and the rest is made up of other metals. This alloying process enhances durability while still maintaining some gold qualities.