Definition
Network-attached storage (NAS) is a dedicated device connected to a local network that serves file-based storage to many clients — in effect, a small file server. Homes use it for photos and media, teams for shared drives and backup targets.
How it works
A NAS is typically a compact computer with multiple drive bays running its own operating system, exposing files over protocols such as SMB and NFS. Internally, the drives are often organized into a RAID array for capacity and redundancy; clients reach it over ordinary Ethernet or Wi-Fi and use it much like a local disk.
Usage
Typical uses include home media libraries and computer backups, shared office documents, and media vaults for video teams. A NAS keeps data on your own hardware — an alternative to public cloud drives.
Related and confusable terms
A NAS is a device form factor built around sharing files over a network; RAID is a redundancy technique commonly used inside it, and is not itself a backup. Unlike a directly installed SSD, the point of a NAS is network sharing and centralized management.