Quorum
Quorum is the minimum attendance needed for a meeting to conduct business. Below it, the meeting can talk, but any vote it takes is open to challenge.
An HOA has two different quorums. A membership quorum, for owner meetings such as the annual meeting, is set by the bylaws or state law, often as a percentage of the total voting interests — owners present in person plus those represented by proxy or absentee ballot usually count. A board quorum is normally a simple majority of the directors in office.
Membership quorums are a common struggle for associations; many bylaws allow an adjourned meeting to reconvene with a lower quorum, and proxies and electronic voting are the usual fixes.