Quorum

Etymology

From Latin "quorum" (of whom), the genitive plural of "qui." The word survives from the Latin wording of old English commissions appointing justices — “quorum vos … unum esse volumus” (of whom we wish you to be one) — where it marked those whose presence was required.

noun · /KWOR-uhm/
The minimum number of members who must be present for a group’s decisions to be valid.
What it names
The threshold that separates a legitimate meeting from an unofficial gathering, protecting a body from being bound by a tiny faction.
Example
Only four of the nine trustees showed up, one short of a quorum, so no vote could be held.
Related idea
Distinct from unanimity or a consensus, which concern agreement among those present; a quorum concerns mere attendance — enough bodies in the room for the meeting to count, whatever they then decide.