Network-Attached Storage (NAS) in its most basic form is a very small PC running an OS just like Windows with the main function to store and manage access to files. Depending on the NAS, it's possible to achieve a whole host of things, including the ability to not only store data but also hook up external services like Plex, which would allow you to transform your NAS into a connected media server.
Full story from the WindowsCentral blog...