Customary law

type or source of law

those aspects of international law that derive from custom

code of conduct transmitted by oral tradition

In law, desuetude (; , ) is a doctrine that causes statutes, similar legislation, or legal principles to lapse and become unenforceable by a long habit of non-enforcement or lapse of time. It is what happens to laws that are not repealed when they become obsolete. It is the legal doctrine that long and continued non-use of a law renders it invalid, at least in the sense that courts will no longer tolerate punishing its transgressors.

body of unwritten rules