What is a NAS?

http://www.lockergnome.com/hardware/2011/09/09/five-ways-to-back-up-your-important-data/

Network-attached storage is typically a storage device that connects directly to your network. In essence, a NAS allows for open (or privileged) access to a shared storage resource. NAS devices typically store media files so they can be played in virtually any room in the house, but can also act as a data hub that securely stores backups of your system(s) in order to prevent loss in the event that the primary system drive fails.

The NAS device I use is a Synology DiskStation, and you can find one like it here:
http://go.tagjag.com/diskstation

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