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.