While live migration has been around since Windows Server 2008 R2, it was greatly improved in WS2012. Previously, a virtual machine could only live migrate (move from one host to another without the interim step of having to shutdown) between nodes of a cluster. In WS2012 virtual machines gained the ability to live migrate between servers regardless of cluster membership.
Live migrate between nodes of a cluster
Live migrate between a cluster node and a stand-alone server
Live migrate between a stand-alone server and a cluster node
NOTE: Both source and destination need to be configured to send and receive live migration.