Endo means looking inside and typically refers to looking inside the body for medical reasons using an endoscope, an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ. Endoscopy can also refer to using a borescope in technical situations where direct line of-sight observation is not feasible.

An endoscope comprises :

• a rigid or flexible tube
• a light delivery system to illuminate the organ or object under inspection. The light source is normally outside the body and the light is typically directed via an optical fiber system
• a lens system transmitting the image to the viewer from the objective lens to the viewer, typically a relay lens system in the case of rigid endoscopes or a bundle of fiber optics in the case of a fiberscope
• an eyepiece
• an additional channel to allow entry of medical instruments or manipulators