A set of customary practices, especially for the operation of a motor vehicle, boat, or aircraft, established to promote efficiency and safety. Often used in the plural.
A set of established rules or practices, usually unstated, intended to minimize confusion or conflict. Often used in the plural: "Great powers ... wishing to avoid war could resort to one of three tools: condominium, spheres of influence or rules of the road"(Charles William Maynes).
