Volume Shadow Copy Service (VSS)
Definition - What does Volume Shadow Copy Service (VSS) mean?
Volume Shadow Copy Service may also be known as Shadow Copy or Volume Snapshot Service.
Techopedia explains Volume Shadow Copy Service (VSS)
The complete copy method makes a full copy of the data on volume, either through hardware or software methods. The differential copy method makes use of blocks, which store the new changes that are done to the original volume. A buffer is then used to logically construct the shadow copy. The differential copy method aids in creating the shadow copies rapidly as it's only writing the changes. However, in order to restore data, the original data volume needs to be present all the time.