Creative brief
A short document that tells a creative team what to make, for whom, why, and what success looks like.
A creative brief answers a handful of questions before anyone starts designing: what's the objective, who is the audience, what's the single thing they should take away, what must be included, what's off limits, where will it run, and when is it due.
One page is usually enough. A brief that runs to six pages is usually a sign nobody decided what matters most. The work gets judged against the brief, so a sharp brief also makes feedback faster and less personal.