borescope

/B AO1 R AH0 S K OW0 P/
noun
  1. 1

    An optical instrument used for seeing inside tight spaces, consisting of a rigid or flexible tube with an optical relay inside so that the view through a lens or window at one end of the tube may be seen from a lens or eyepiece in the opposite end of the tube.

Source: https://en.wiktionary.org/wiki/borescope