(n.) An internally lighted optical instrument for viewing normally concealed or inaccessible components. Source: Lock Industry Standards and Training (LIST) Council

An optical instrument with an illuminating lamp for inspecting the inside surface of OCTG.

A device for internal inspection of difficult access locations such as pipes, engines, rifle barrels and pipes. Its long narrow tube contains a telescope system with a number of relay lenses. Light is provided via the optical path or fiber bundles. A 45-degree mirror at the end allows inspection of tube walls

A borescope is an optical device consisting of a rigid or flexible tube with an eyepiece on one end, an objective lens on the other linked together by a relay optical system in between. The optical system is usually surrounded by optical fibers used for illumination of the remote object and a rigid or flexible protective outer sheath. The remote object is illuminated and an internal image formed by the objective lens is relayed to the eyepiece which magnifies the internal image and presents it to the viewer's eye.