newsgroup definition

Newsgroups are organized into subject hierarchies, with the first few letters of the newsgroup name indicating the major subject category and sub-categories represented by a subtopic name. Many subjects have multiple levels of subtopics. Some major subject categories are: news, rec (recreation), soc (society), sci (science), comp (computers), and so forth (there are many more). Users can post to existing newsgroups, respond to previous posts, and create new newsgroups.

Newcomers to newsgroups are requested to learn basic Usenet netiquette and to get familiar with a newsgroup before posting to it. The rules can be found when you start to enter the Usenet through your browser or an online service. You can subscribe to the postings on a particular newsgroup.

Some newsgroups are moderated by a designated person who decides which postings to allow or to remove. Most newsgroups are unmoderated.

Usenet is the set of people who exchange articles tagged with one or more universally-recognized labels, called "newsgroups" (or "groups" for short).
There is often confusion about the precise set of newsgroups that constitute Usenet; one commonly accepted definition is that it consists of newsgroups listed in the periodic "List of Active Newsgroups" postings which appear regularly in news.lists.misc and other newsgroups. A broader definition of
Usenet would include the newsgroups listed in the article "Alternative Newsgroup Hierarchies" (frequently posted to news.lists.misc). An even
broader definition includes even newsgroups that are restricted to specific geographic regions or organizations. Each Usenet site makes its own decisions about the set of groups available to its users; this set differs from site to site.

reference: http://www.faqs.org/faqs/usenet/what-is/part1/