Backups and snapshots are different methods of attaining data redundancy. A snapshot is an "image" of a server at a point in time, stored locally to the virtual host. This is important to note, as a backup is stored off of the host. While they both accomplish similar tasks, snapshots are typically used to revert changes made to a virtual machine when attempting new configurations. Backups are intended to preserve information stored on a server or database for future restoration if needed.
In computer systems, a snapshot is the state of a system at a particular point in time. The term was coined as an analogy to that in photography. It can refer to an actual copy of the state of a system or to a capability provided by certain systems.