Usually ground rules.basic or governing principles of conduct in any situation or field of endeavor: the ground rules of press conferences.
Sports. any of certain rules specially adopted, as in baseball and softball, for dealing with situations or circumstances arising chiefly from the particular nature of the playing area or the interference of spectators.
Basic procedures of conduct, as in The press secretary sets the ground rules for all of the President's press conferences. The term comes from baseball, where it refers to specific rules for a particular ballpark, which are based on special conditions such as a very high outfield fence or a field obstruction of some kind. It began to be transferred to more general use in the mid-1900s.