A buoyancy control device (BCD) is an essential piece of equipment used in scuba diving. It allows divers to control their buoyancy underwater, helping them to ascend, descend, or maintain a specific depth. The BCD is typically worn like a vest and is equipped with air bladders that can be inflated or deflated using a regulator connected to a tank of compressed air. When a diver wants to rise, they can add air to the BCD, increasing their buoyancy. Conversely, releasing air from the BCD allows them to sink. Proper use of a BCD is crucial for safe diving, as it helps divers manage their position in the water column effectively.