In the description of the VirtualSystemType property of Msvm_VirtualSystemSettingData http://msdn.microsoft.com/en-us/library/hh850257(v=vs.85).asp we see :
"Microsoft:Hyper-V:Snapshot:Recovery" - A snapshot of a recovery virtual machine.
"Microsoft:Hyper-V:Snapshot:Realized" - A snapshot of a realized virtual machine.
"Microsoft:Hyper-V:Snapshot:Planned" - A snapshot of a planned virtual machine.
What are recovery, realized and planned Vm's types? can't finnd description.