A telescope is an instrument designed for the observation of remote objects.
The term usually refers to optical telescopes, but there are telescopes for most of the spectrum of electromagnetic radiation and for other signal types.
An optical telescope gathers and focuses visible light and other electromagnetic radiation.
Telescopes increase the apparent angular size of distant objects, as well as their apparent brightness.
Telescopes work by employing one or more curved optical elements - lenses or mirrors - to gather light or other electromagnetic radiation and bring that light or radiation to a focus, where the image can be observed, photographed or studied.
Optical telescopes are used for astronomy and in many non-astronomical instruments including theodolites, transits, spotting scopes, monoculars, binoculars, camera lenses and spyglasses.