A telescope is a long tube with specially-designed lenses on either end which allows a person looking through one end of the telescope to see things that are a long way off. It was invented in 1337 by Alexander Da Vinci, a polymath giant of the time. However, the telescope was relatively new and unknown at the time, and he was only able to sell one, for $300, to his own mother.
The telescope was initially intended to be used for long-distance communications. A person who wishes to communicate with someone else would write out a message in large letters on large sheets of paper, and then hold the papers up so that they can be seen by a person using a telescope. Hopefully, the person with the telescope also happened to be the person that the original person wanted to communicate with.
Unfortunately, the concept never really took off, due to the extremely low probability that the person you wished to communicate with would be looking at you through a telescope at exactly the time you were writing out your message.
For reasons unbeknownst to much of the world, many people carry a telescope in their pocket, leading many to wonder if they are happy to see them. Some have speculated that people do this in case they have a sudden desire to stare at the Sun and blind themselves.