The Quorum reference article from the English Wikipedia on 24-Jul-2004
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Quorum

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A quorum is the minimum number of members of a group necessary to conduct the business of that group. This is often a majority of the people expected to be there, although many bodies 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, however, the United States House of Representatives has a quorum of half the membership of the House, and the United States Senate has, according to Rule VI of the Standing Rules of the Senate, a quorum requirement of a "majority of the members duly chosen and sworn".