World bible
Also said as Story bible, Series bible, Lore document
The reference document that holds the true answers about your world: the timeline, the names, the rules, how things are spelled. It is written for the team, not for players.
Two writers will each answer an unasked question differently, and the bigger the team, the sooner it happens. A bible settles it once, as long as someone keeps it up to date.
Say it
“Before the two writers start, put a one-page world bible together: the calendar, how magic is paid for, who rules what, and how every place name is spelled. Whoever finds a gap fills it in the bible first.”
Where you’ve seen it
Halo has a story bible, started at Bungie and carried on at 343 Industries, kept so that the games and books agree. Outside authors are sent the parts they need for their own work.
Not to be confused with game design document
A design document says how the game works and what you will build. A world bible says what is true in the fiction, whether or not any of it is ever shown.