The Free On-line Dictionary of Computing (30 December 2018):

Undernet

    An Internet Relay Chat network dating from the
   1990s, when it broke away from the main (still larger) IRC
   network, EFNet.

   (http://undernet.org/).

   The History of the Undernet
   (http://www2.undernet.org:8080/~cs93jtl/unet_history.txt).

   (1995-11-09)