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”