A telescope is a tool that astronomers use to observe the sky. Even though telescopes are best used for observing the heavens, telescopes can also be used to observe far away, and hopefully more earthly, objects. Also good for watching the night sky are Binoculars.
As technology has become more and more advanced, different types of telescopes have been invented such as the X-Ray telescope, Gamma-ray telescope, and so forth.
In math, the term telescope means that after much simplification and cancellation, the answer is something very simple, i.e. 1, 1/5, etc.