Final answer:
A quorum is the minimum number of members required to be present for Congress to conduct business, typically a majority. If a quorum is not present, business can continue unless a 'quorum call' is issued, which would necessitate the presence of a majority. Supermajorities are sometimes required for significant legislative actions.
Step-by-step explanation:
A quorum is defined as the minimum number of members that must be present for the House or Senate to conduct official business, which is typically a majority of the members. According to the US Constitution, if less than a majority of members are present, business can still proceed; however, any member can issue a 'quorum call' which would require either a majority of members to show up or the House to temporarily adjourn. Therefore, for business to be transacted officially, a quorum is necessary. In the case of important decisions, like constitutional amendments or ending a filibuster in the Senate, a supermajority may be required, which is a higher threshold than a simple majority.