Adjectives

(a)unwrittenbased on custom rather than documentation“an unwritten law”, “rites...so ancient that they well might have had their unwritten origins in Aurignacian times” (J.L.T.C.Spence)
(s)oral, unwrittenusing speech rather than writing“an oral tradition”, “an oral agreement”
(s)ad-lib, spontaneous, unwrittensaid or done without having been planned or written in advance“he made a few ad-lib remarks”