BCD stands for buoyancy compensation device. These handy and essential bits of equipment allow a diver to offset their negative buoyancy by adding air from the tank to the BCD while underwater. They’re also essential on the surface for maintaining positive buoyancy.
BCDs have come a long way since the old-school Fenzy collars which featured only an oral inflate function and a single air bladder which was worn around the neck. Today’s models are incredibly comfortable, user-friendly, and come in a variety of styles.