Most often, when someone talks about a filesystem or file system, they're referring to disk filesystems such as NTFS, FAT, ext2, ext3, ext4, ISO 9660 and many others but can also refer to network file systems such as CIFS (Common Internet File System aka Samba) and NFS. A filesystem is a specially-designed database of files, their disk location, definition and attributes. Everything on a Unix or Linux filesystem is a file: Directories, processes, links, programs, and device references. All files.