house rule

house rule (plural house rules)

1. A rule adopted by a particular establishment.
   • 2000, Charles Staples Magnum, The Legal Status of the Negro:

     A house rule was put into effect which set aside certain hours when the hall was to be used by white patrons only.

   • 2000, Anthony Bailey, America Lost and Found: An English Boy's Wartime Adventure in the New World:

     There were a couple of strict house rules: no playing on the billiard table, which we had damaged twice; and no talking in bed.

2. A rule used in playing a game that is not part of the official ruleset.