QUORUM

(noun) the minimum number of persons required at a board meeting or general meeting in order for business to be conducted. E.g.: "The charter required a quorum of two-thirds of the shareholders to vote on new issues of shares."

Other forms of the word/phrases
quorate (adjective) - having a quorum. "An election will be held at the next quorate board meeting."
have a quorum: "The meeting could not be held because we did not have a quorum."
constitute a quorum: "The board could not resolve on the new share issue because there were not enough members present to constitute a quorum."
Source: Translegal