commonrule

2. A rule that applies to all members of a community equally.

The village commonrule said no one could cut trees in the shared forest.

3. A widely accepted principle used as a default when nothing else is specified.

As a commonrule, meetings start at nine unless someone says otherwise.

4. A basic rule shared across many games or activities.

The commonrule of the tournament was that every player had to shake hands first.