Toaru (とある lit. "A Certain"?) or the Toaru series (とある「シリーズ」 lit. "A Certain Series"?) is the official Japanese shorthand used by Dengeki and others to refer to the whole Toaru Majutsu no Index franchise in promotional materials, articles, and interviews.
It is a reference to the idiosyncratic naming scheme the franchise uses for its series and other properties. How all the official series from the franchise has "Toaru" in the title, comprised of the first three hiragana characters (とある).
- Raildex - English equivalent that is used by the fandom instead.