Definitions for unwrittenʌnˈrɪt n
Random House Webster's College Dictionary
not actually formulated or expressed; customary; traditional.
not written; not put in writing or print; oral:
an unwritten agreement.
containing no writing; blank.
Origin of unwritten:
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
using speech rather than writing
"an oral tradition"; "an oral agreement"
ad-lib, spontaneous, unwritten(adj)
said or done without having been planned or written in advance
"he made a few ad-lib remarks"
Spoken or otherwise communicated other than in writing.
Implicit or understood but not formally articulated.
It's an unwritten law that you lock the gate when you leave the swimming pool.
not written; not reduced to writing; oral; as, unwritten agreements
containing no writing; blank; as, unwritten paper