A disk “snapshot” is a copy of the virtual machine disk file (VMDK) at a certain point in time. It preserves the disk file system and system memory of your VM by enabling you to revert to the snapshot in case something goes wrong. Snapshots can be real lifesavers when upgrading or patching applications and servers. This article will go over everything you need to know about using snapshots with VMware, including what they are, how they work and advanced techniques.
Another must read to uderstand snapping. Thanks Eric