Esperantujo or Esperantio is a term (meaning "Esperantoland") used by speakers of the constructed international auxiliary language Esperanto to refer to the Esperanto community and the activities going on in the language. When two people are speaking Esperanto, they are said to be "in" Esperantujo.
The word is formed analogously to country names. In Esperanto, the names of both lands and nation states were traditionally formed from the ethnic name of their inhabitants plus the suffix -ujo, so for example "France" was Francujo, from franco (a Frenchman).
The term most analogous to Francujo would be Esperantistujo (Esperantist-land). However, that would convey the idea of the physical body of people, whereas using the name of the language as the basis of the word gives it the more abstract connotation of a cultural sphere.
Currently, names of nation states are often formed with the suffix -io traditionally reserved for deriving country names from geographic features, so now Francio, and recently the form Esperantio has been used i.a. in the Pasporta Servo and the Esperanto Citizens' Community.
In 1908, Doctor William Molly attempted to create an Esperanto nation in Neutral Moresnet known as "Amikejo" (land of great friendship). What became of it is unclear, and Neutral Moresnet was annexed to Belgium in the Treaty of Versailles, 1919. 
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