A "quorum" is the minimum number of individuals who must be present in order for business to be conducted. Associations have quorums for both unit owner meetings and board member meetings.
Unless your bylaws state otherwise, the quorum for a unit owner meeting is 20% of members by ownership percentage. The quorum for a board meeting is a majority of the board members (at least 50%). If these minimums are not met, voting cannot take place at a meeting.