Question

what is a periscope?​

Answer 1

Explanation:

device like a long tube, containing mirrors which allow you to see over the top of something, used especially in a submarine to see above the surface of the sea

Answer 2

Answer:

A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with mirrors at each end set parallel to each other at a 45° angle.

Simpler one:

A device like a long tube, containing mirrors which allow you to see over the top of something, used especially in a submarine to see above the surface of the sea.