Sun's Network File System (NFS) has become a standard for using remote disks not only in the Unix- but in the whole TCP/IP-world. The idea is quite simple: one host "exports" a directory, and other hosts can mount that directory and access it and its subdirectories.
When users from several machines want to use the same set of files, special care has to be taken for the user-ids and group-ids the files have: UID and GID of the users must be unique across the (NFS-)network, or one won't be able to read a file on one machine created on another one (where the same user had a different UID).
There are also some security-mechanisms built in to prevent unauthorized
machines from mounting directories or which prevent root-access to files
from remote machines. I won't introduce those mechanisms here and I'll
assume no special measures for mounting/exporting filesystems here. If you
need to know about those mechanisms, please read mount(8),
exports(5).
See RFC 1094 for a description of NFS.