Lyoko is a virtual world inside an advanced supercomputer within a factory.  You can enter the world of Lyoko by the process of virtualisation, where a person from the real world is transferred into the virtual world.  The world of Lyoko is divided into five sectors, the Ice Sector, Mountain Sector, Forest Sector, Desert Sector, and Sector 5.  Because of X.A.N.A., Lyoko has become a dangerous place.  But Lyoko warriors fight to defeat X.A.N.A. and its minions.