Quorum

In law, a quorum is the minimum number of members of a deliberative body necessary to conduct the business of that group. By default, this is a majority of the people expected to be there, although many bodies may have a much lower quorum. For instance, the House of Lords can decide on procedural issues if a mere three members are present. By contrast, according to Article One of the United States Constitution, the United States House of Representatives and the United States Senate each have a quorum of a majority of their respective members. The Senate has the additionl requirement in Rule VI of its standing rules of a "majority of the members duly chosen and sworn."

In biology, a quorum is the number of bacteria required for a certain behaviour to occur. See quorum sensing