NFS Network File System
Classic way to mount a remote filesystem as if it were local — Sun, 1984.
NFSv4 is modern: stateful, Kerberos-secured, better performance. Competitor: SMB (Windows world). Common in: Linux clusters, ESXi storage, home NAS. Scalable shared filesystems on K8s: NFS by default, or CSI drivers for EFS/CephFS.