Wikipedia Day is celebrated on January 15, 2018. January 15 is known as Wikipedia Day to Wikipedians. On this date in the year 2001, the wiki-based Wikipedia project went public after spending five days on Nupedia. Wikipedia Day has been celebrated, both online and offline, for several years.
Wikipedia is a collaboratively edited, multilingual, free Internet encyclopedia that the non-profit Wikimedia Foundation supports. Volunteers worldwide collaboratively write Wikipedia's 30 million articles in 287 languages, including over 4.4 million in the English Wikipedia. Anyone who can access the site can edit almost any of its articles.
Jimmy Wales and Larry Sanger launched Wikipedia on January 15, 2001, the latter creating its name Wikipedia, from a portmanteau of wiki (a type of collaborative website, from the Hawaiian word wiki, meaning "quick") and encyclopedia. (With material from: Wikipedia)