Wikipedia is a free, multilingual, open-source encyclopedia that is available on the Internet. It is a collaboratively edited encyclopedia, meaning that anyone with an internet connection can edit and contribute to the articles. Wikipedia is based on the principle of a wiki, which allows multiple users to edit, add to, and improve the content of articles. The articles are written by volunteers from around the world, and are overseen by a small group of volunteer editors known as administrators. Wikipedia is not considered to be a reliable source of information as the contents in Wikipedia can be edited by anyone and there is no guarantee of the accuracy of the information. But it's widely used as a starting point for research and for general information on a wide range of topics. It is one of the most visited websites in the world and is available in over 300 languages.