The World of Kamen Rider is the version of reality where Kamen Rider takes place. It is where Shocker executive Ambassador Hell of Dai-Shocker originally came from.
The World of Kamen Rider is also used in Shuriken Sentai Ninninger Vs. Kamen Rider Drive Spring Vacation Combining Special by Kyuemon Izayoi to refer to the Kamen Riders' prime reality where the characters from Ninninger temporarily cross into due to the History Modifying Machine altering reality. Previously, in the movie Super Hero Taisen, Doktor G describes Dai-Shocker to the Go-Busters as the union of organizations from the Rider World.
Material related to the movie also uses the names Kamen Rider World to describe this version of reality where all the Kamen Rider TV shows take place. The movie itself doesn't specify where the action is taking place most of the time, but it features characters going from one location to another through Kamen Rider Decade's dimensional walls.
Related Post : Source : wikipedia / kamenrider.wikia
