A method of broadcasting messages to everyone who is interested in a given narrow
topic. There are currently about 4000 topics. Only one copy of the message is sent to
each computer supporting people interested in that topic. In contrast, a mail list
would send individual copies to each user on the list. Usenet topics are for large
global, public, communities of interested users. Mail lists are for smaller private
groups. Forums are usually hosted on a single web server.
Usually called newsgroups.