The image shows a bicycle rear tail light. This type of light is designed to be mounted on a bicycle's seat post to increase visibility and safety for the rider.
It is often referred to as a "twin-eye" or "dual LED" light due to its design. 
It typically features multiple lighting modes, such as steady and flashing, to suit different riding conditions. 
The light is often waterproof and comes with a silicone mounting strap for easy installation and removal. 
These lights are super bright and have a wide beam angle to ensure the cyclist is seen by others, day or night