A NAS (Network Attached Storage) is a mass storage device connected to a computer network and works as a file server.
The device can be composed by a series of hard disk drives and generally run Linux (Embedded) OS.
Main manufacturers are Synology, QNAP, Western Digital, Seagate.
The connection to the network is made with ethernet cable, but there are also models with WiFi.
In NAS we can find other connections available, USB (2.0/3.0) ports.
Let see the advantages to use a NAS in an home environment.
Centralized file storage
All files are available at any moment and from any device on multiple platforms. For example you can access files from a Windows PC, or Mac or Linux, perform data backup to the NAS.
NAS can work as multimedia server for UPnP/DLNA enabled devices. Generally you can easily enable this feature from a control panel provided to the user.
Once enabled you can stream files (video, audio, photo playback) to compatible devices (eg. smart tv, consoles).
NAS can work as iTunes server, you just must enable this feature from the control panel.
NAS can assume the role of a print server and replace expensive network printers.
Sync with cloud services
NAS, within specific apps/services, can interface with various cloud services (eg. Google Drive, Dropbox) and sync files.
Various NAS provides apps/services that allows to download files using various protocols (eg. HTTP, FTP, Torrent, eMule) directly into device.