File created by VMware virtualization software; saves the virtual machine (VM) data for a snapshot, which is a frozen state of the VM saved at a particular point in time; can be one of several different snapshots used by the virtual machine; saved with a .VMSD file, which contains the metadata for the snapshot.

VM snapshots are useful for saving a fresh installation of a guest operating system (OS) so that users can revert back to a clean OS install even after applications have been installed. NOTE: You do not need to open VMSN files manually since snapshots can be saved and loaded from within the VMware software's user interface.