Encyclopedia
An encyclopedia (or, the less-frequently used encyclopaedia) is a book, a collection of books, or electronic media, that contains comprehensive information regarding all human knowledge or in a particular field, and is used for reference purposes. Famous encyclopedias include Encyclopaedia Britannica Eleventh Edition (1911), Encyclopaedia Britannica, Encarta, World Book, Encyclopedia Americana, Wikipedia and Citizendium. Many specialized encyclopedia have appeared, such as the Catholic Encyclopedia and Jewish Encyclopedia. Since the 1990s electronic publication has increasingly replaced print. Indeed there has never been a print version of Encarta, Wikipedia or Citizendium. One new encyclopedia on the web is the Unitarian-Universalist Encyclopedia.