An endoscope is a long tube used in hospitals. Doctors need to see inside your bodies and they can use the endoscope to help them. Doctors put the tube into your body, either down into your tummy, or up your bottom or they may make a little cut in your skin and put the endoscope in there. Using an endoscope means that doctors don't need to make big cuts to go inside the body. Inside the endoscope are many optical fibres. There are 2 different groups of optical fibres in the endoscope.
Health is not the only context where endoscopes are used. When police are investigating a bomb they can use endoscopes to see inside a bomb because they can't get near. Endoscopes can also be used by garages to inspect inside engines.
an endoscope
Picture from Wikimedia