A private server is identical to that of a public server, but contains access restrictions (network ACLs or similar) limiting the scope of those who can use it. Usually these servers are available on an invite-only basis, but may be available to the general public upon contact. They are accessed via a telnet or SSH client.
List of private servers
|nethack.koitsu.org||Sylmar, California, United States||Invitefirstname.lastname@example.org|