Network Attached Storage (NAS) is a Network Appliance that is a dedicated server, also referred to as an appliance, used for file storage and sharing. NAS is a hard drive attached to a network, used for storage and accessed through an assigned network address. It acts as a server for file sharing but does not allow other services (like emails or authentication). It allows the addition of more storage space to available networks even when the system is shutdown during maintenance.
NAS is a complete system designed for heavy network systems, which may be processing millions of transactions per minute. NAS provides a widely supported storage system for any organization requiring a reliable network system.
Source: https://www.techopedia.com/definition/26197/network-attached-storage-nas