Borescope
A borescope (occasionally called a boroscope, though this spelling is nonstandard) is an optical instrument designed to assist visual inspection of narrow, difficult-to-reach cavities, consisting of a rigid or flexible tube with an eyepiece or display on one end, an objective lens or camera on the other, linked together by an optical or electrical system in between. The optical system in some instances is accompanied by (typically fiberoptic) illumination to enhance brightness and contrast.