VSS – Volume Shadow copy Service – also known as Microsoft shadow Copy. This is a Windows Server data backup feature for creating consistent point-in-time copies of data (called shadow copies). It enables the Windows OS or applications to take “point-in-time snapshots” of a disk volume without locking the filesystem. This can be done periodically and it means Windows or the application can run a backup against the volume without data changes acurring during a normal backup window and not being captrured by the backup process.