A quorum is the minimum number of members of a group necessary to constitute the group at a meeting. In a deliberative assembly, a quorum is necessary to conduct the business of that group. According to Robert's Rules of Order Newly Revised, the "requirement for a quorum is protection against totally unrepresentative action in the name of the body by an unduly small number of persons." In contrast, a plenum is a meeting of the full body. A body, or a meeting or vote of it, is quorate if a quorum is present.

Robert's Rules of Order, often simply referred to as Robert's Rules, is a manual of parliamentary procedure by U.S. Army officer Henry Martyn Robert. "The object of Rules of Order is to assist an assembly to accomplish the work for which it was designed [...] Where there is no law [...] there is the least of real liberty." The term Robert's Rules of Order is also used more generically to refer to any of the more recent editions, by various editors and authors, based on any of Robert's original editions, and the term is used more generically in the United States to refer to parliamentary procedure. It was written primarily to help guide voluntary associations in their operations of governance.