Rules of behavior that are defined both formally and informally are

Rules of behavior that are defined both formally and informally are norms. 
Norms refer to rules - rules that need to be followed if we want to be accepted by our community. Failing to follow such rules will make the community fear us, or ostracize us if we don't conform. Norms can either be written (when they become laws), or they can be informal norms which are just known to exist, but aren't actually written anywhere specifically.