The Network File System (NFS) protocol is a TCP/IP application that supports networked filesystems. It provides transparent access to shared filesystems across networks.
NFS lets a client workstation operate on files that reside on a server across a variety of NFS-compliant operating systems. File access calls from a client are converted to NFS protocol (see RFC 1094 and RFC 1813) requests, and are sent to the server over the network. The server receives the request, performs the actual filesystem operation, and sends a response back to the client.
In essence, NFS lets you graft remote filesystems — or portions of them — onto your local namespace. Directories on the remote systems appear as part of your local filesystem, and all the utilities you use for listing and managing files (e.g. ls, cp, mv) operate on the remote files exactly as they do on your local files.