micronation

noun
  1. an entity, typically existing only on the internet or within the private property of its members, that lays claim to sovereign status as an independent nation, but which is unrecognized by real nations
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012