ground rule

1 ENTRIES FOUND:
ground rule noun
plural ground rules
ground rule
noun
plural ground rules
Britannica Dictionary definition of GROUND RULE
[count]
1 
: a basic rule about what should be done in a particular situation, event, etc. — usually plural
2 
chiefly US, sports : a special rule about how a game is played on a particular field, court, or course — usually plural