A NAS (Network Attached Storage) is a device with several disks that connects to the network and makes files available to authorized users. It is simpler than a full server and is mainly used for storing files.
A NAS is a common place for backups. But if every copy lives only on the office NAS, a fire, theft or ransomware can damage the original and the copy together — so one copy should be kept off-site.
Example
A design studio stores large files on a NAS, backs it up automatically every night and sends one copy to the cloud.