Definition
The minimum number of members who must participate for a meeting's votes and business to be valid.
Quorum is the minimum level of participation required for a meeting to conduct official business. Your bylaws set the threshold, usually as a percentage of the membership.
Without quorum, an election can't be certified and votes requiring member approval can't pass — the business simply waits. Failing to reach quorum is the single most common reason HOA meetings and elections fall apart. Making participation easy (including online) and collecting proxies in advance are the best ways to reach it reliably.