means The smallest number of members who must be present at a meeting for its decisions and votes to be officially valid.

from Straight from Latin, where quorum literally means "of whom" — the genitive plural of qui, "who." It survives from old English legal commissions written in Latin that named certain people whose presence was required, phrased something like "of whom we wish you to be one" (quorum vos... unum esse volumus). The crucial word in that formula was quorum, and over time it stopped meaning "of whom" and started meaning the required group itself.