The term ground rules refers specifically to a project utilization tool that is typically discussed and implemented by the project team and the project team leader at a very early phase of the project, if not possibly even before the project has been formally discussed in any other fashion whatsoever. The ground rules can specifically include a list of any and all behaviors that are considered to be acceptable and unacceptable in the context of the management of the project. The goal behind project ground rules is to improve the relationships between the different individual members of the project team. The improvement of the relationships can possibly help the team work better, more efficiently, and more cost effectively. It also can allow for improved communication among the project team members, which can in turn have a cyclical effect, leading to even more improved work relationships and ultimately, leading to a better end result for the project team.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.