What does the sash over Prince William's wedding uniform indicate?

The sash worn by Prince William during his wedding to Catherine Middleton indicates that he is a member of the British royal family and signifies his status as a Knight of the Order of the Garter, one of the oldest and most prestigious chivalric orders in the UK. The blue sash is a symbol of his rank and honors conferred upon him. Additionally, it serves to distinguish him within the formal military uniform he wore for the ceremony.