Usenet (Users' Network) is a bulletin board shared among many computer
systems around the world. Usenet is a logical network, sitting on top
of several physical networks, including UUCP, BITNET, and the
Internet. Sites on Usenet include many universities, private
companies, and research organizations. Current estimates indicate
that there are over two million participants at over 45,000 Usenet
sites in over fifty countries, with more users and sites joining every
day. Most are running the UNIX 
operating
system, although the number of non-UNIX sites, e.g.
VMS sites and PCs, is increasing.