1. The minimal number of officers and members of a committee or organization, usually a majority, who must be present for valid transaction of business.
2. A select group.
3. The minimal density of bacterial cells that results in altered gene expression in a population of bacteria.
[Middle English, quorum of justices of the peace, from Latin quōrum, of whom (from the wording of a commission naming certain persons as members of a body), genitive pl. of quī, who; see kwo- in the Appendix of Indo-European roots.]
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