These are usually the rules followed in ones house that a particular game is being played in. These rules will always change from house to house and are sure to always cause a 10 minute argument/debate over them. These rules are known to be made up during the actual game.
For example: if you are playing pool in one person's house, his "house rules" might be that whoever makes the 8 On The Break wins automatically whereas the house rules of another person's house might be whoever makes the 8 On The Break loses automatically.
af D. Ferrel 30. september 2003