ROBERT RULES!
What exactly is quorum?

Answer:
A Quorum of an assembly is such a number as must be present in order that business can be legally transacted. The quorum refers to the number present, not to the number voting. The quorum of a mass meeting is the number present at the time, as they constitute the membership at that time. The quorum of a body of delegates, unless the by-laws provide for a smaller quorum, is a majority of the number enrolled as attending the convention,
not those appointed. The quorum of any other deliberative assembly with an enrolled membership (unless the by-laws provide for a smaller quorum) is a majority of all the members. In the case, however, of a society, like many religious ones, where there are no annual dues, and where membership is for life (unless it is transferred or the names are struck from the roll by a vote of the society) the register of members is not reliable as a list of the bona fide members of the society, and in many such societies it would be impossible to have present at a business meeting a majority of those enrolled as members. Where such societies have no by-law establishing a quorum, the quorum consists of those who attend the meeting, provided it is either a stated meeting or one that has been properly called.. http://www.robertsrules.com