Monocular– A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and usually prisms, the application of prisms resulting in a lightweight, compact telescope. Volume and weight are less than half those of binoculars of similar optical properties, making a monocular easy to carry, and also proportionally less expensive. Monoculars produce 2-dimensional images, while binoculars add perception of depth (3 dimensions), assuming one has normal binocular vision.

Monocular – Wikipedia

https://en.wikipedia.org/wiki/Monocular

A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and usually prisms, the application of prisms resulting in a lightweight, compact telescope. Volume and weight are less than half those of binoculars of similar optical properties, making a monocular easy to carry, and also proportionally less expensive. Monoculars produce 2-dimensional images, while binoculars add perception of depth (3 dimensions), assuming one has normal binocular vision.