Dynamic Quorum is the ability of a Windows Server failover cluster to recalculate quorum when nodes fail or shut down sequentially.
In a failover cluster, quorum is the number of elements that must be online for that cluster to continue running. As a new feature in Windows Server 2012, Dynamic Quorum works on two conditions: the first condition is that the cluster has already achieved quorum; the second condition is that sequential nodes have failed. When nodes shut down sequentially, Dynamic Quorum allows the cluster to continue running with less than a majority of active nodes.
Administrators can modify and view Dynamic Quorum with PowerShell cmdlets.