ground rule noun
plural ∼ rules [count] 1 : a basic rule about what should be done in a particular situation, event, etc. — usually plural ▪ We need to lay out the ground rules for tonight's meeting. 2 chiefly US, sports : a special rule about how a game is played on a particular field, court, or course — usually plural ▪ The coaches and umpires discussed the ground rules.
