I'm pretty sure when SysAdmins talk about VSS they aren't talking about Visual Source Safe...
Volume Shadow Copy Service.
It takes a snapshot of files so they can be backed up even while they're in use. It ensures that the file is not modified between the start and end of the backup, but can't ensure that the file is in an actually usable state should it need to be restored (for instance, a database file may be in mid-row modification when the snapshot is taken so the file itself is in a consistent state, but the application using it chokes on the half-finished edit).
1If the application has a "VSS Writer" registered with the system, it does a quick bit of work to ensure that the file is usable upon restoration. Microsoft SQL Server and Exchange have VSS Writers installed by default, as do many third-party applications. "Real" databases can recover from yanking the power cord in any case, so this is just extra safety. Apr 11, 2011 at 14:33
It's the Volume Shadow Copy Service.
Shadow Copy ?
Volume Shadow Copy, its used for backing files up while they're in use.
visual source safe is a configuration managament tool used for storage of project related documents,etc for future purpose.