Usenet is a world-wide
distributed discussion system. It consists of a set of
newsgroups with names that are classified
hierarchically by subject.
Articles or messages are posted to these newsgroups by people on computers with the appropriate software -- these articles are then broadcast to other interconnected computer systems via a wide
variety of networks. The articles generally expires in a few days, but now there are a number of usenet archives that keep the messages for posterity.
Some newsgroups are moderated; in these newsgroups, the articles are first sent to a moderator for approval before appearing in the newsgroup.
Usenet is available on a wide variety
of computer systems and networks, but the bulk of modern Usenet traffic is transported over either the Internet or UUCP.
after http://www.faqs.org/usenet/
http://www.faqs.org/faqs/usenet/what-is/part1/