Network File System is a distributed file system protocol originally developed by Sun Microsystems in 1984, allowing a user on a client computer to access files over a computer network much like local storage is accessed
NFS (Network File System) is a protocol allowing remote access to a filesystem through the network. All Unix systems can work with this protocol; when Windows systems are involved, Samba must be used instead. NFS is a very useful tool but, historically, it has suffered from many limitations, most of which have been addressed with version 4 of the protocol. The downside is that the latest version of NFS is harder to configure when you want to make use of basic security features such as authentication and encryption since it relies on Kerberos for those parts. And without those, the NFS protocol must be restricted to a trusted local network since data goes over the network unencrypted (a sniffer can intercept it) and access rights are granted based on the client's IP address (which can be spoofed).