Loading zone
A loading zone is a flat object that transports Mario to a different world if he comes into contact with it, generally located within doorways and other transitional paths.
Properties
Most commonly located in doorways, loading zones generally appear solid black or white, and trigger a screen transition of a spinning hat upon entering them. While most loading zones transport Mario to a different scene, there are a few in the game that transport Mario to a world that seems unconnected, but is in fact located in a distant area within the same scene as the original world.