Wikipedia

Definition: Launched in January 2001, by Jimmy Wales and Larry Sanger, Wikipedia is now the largest and fastest growing encyclopedia online. In fact it is one of the world’s ten most visited websites.As of September 2007 the English Edition of Wikipedia had a massive 4.5 million articles and over 32 million pages, making it around 70 times the size of the Encyclopedia Britannica.

FirstClickSEO Commentary: Wikipedia is multilingual and is currently available in 287 languages. Operated by the Wikimedia Foundation, a non-profit organization, it is a collaboratively written by volunteers around the world.