The ceremonial sash worn across the chest by Klingon warriors, and by Worf over his Starfleet uniform throughout his service on the Enterprise-D and Deep Space 9.
The baldric is a broad band worn from one shoulder to the opposite hip. It is a mark of a Klingon warrior's standing and may carry the emblem of his house. Worf is permitted to wear his with the Starfleet uniform as an acknowledgement of his heritage.
He wears a cloth sash in the first season of The Next Generation and a heavier one of linked metal from the second season onward, which he keeps through Deep Space Nine and the films.
The baldric plays a small part in the episode Conundrum. When the crew lose their memories, Worf looks at his elaborate decoration, concludes that he must be in command and takes the captain's chair, until the ship's records show otherwise.