A lifebuoy is a throwable, inherently buoyant safety device designed to keep a person afloat in a man-overboard emergency, typically shaped as a ring or horseshoe, often brightly colored for visibility. It is a critical piece of sailing equipment, meant to be quickly released from the rails and often connected to a buoyant lifeline or a self-igniting light.

Key Features and Usage:
Purpose: Provides immediate buoyancy to a person in the water.

Shapes: Typically circular or horseshoe-shaped.

Visibility & Storage: Must be a conspicuous color and secured to railings for rapid deployment.

Components: Often features a grab line around the circumference and can be attached to a dan buoy for improved visibility.

Requirements: Generally at least 610 mm in diameter and often required on vessels over 9 meters.

Lifebuoys are sometimes referred to as life rings, life preservers, or lifesavers, and are often paired with a dan buoy or a light for nighttime rescues.