unwritten

adjectives

based 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
unwritten
antonym
written
is similar to
based on common law
"a common-law right"
common-law
using speech rather than writing
"an oral tradition"; "an oral agreement"
oral, unwritten
said or done without having been planned or written in advance
"he made a few ad-lib remarks"
ad-lib, spontaneous, unwritten