quorum

The number of Senators that must be present for the Senate to do business. The Constitution requires a majority of Senators (51) for a quorum. Often, fewer Senators are actually present on the floor, but the Senate presumes that a quorum is present unless the contrary is shown by a roll call vote or quorum call.

For a failover cluster, the number of elements that must be online for a given cluster to continue running. The elements relevant in this context are nodes or, in some cases, a witness disk or witness file share.

See cluster quorum.