A newsgroup is a discussion about a particular subject consisting of notes written to a central Internet site and redistributed through Usenet, a worldwide network of news discussion groups. Usenet uses the Network News Transfer Protocol (NNTP).
Newsgroups are organized into subject hierarchies, with the first few letters of the newsgroup name indicating the major subject category
Some major subject categories are: news, rec (recreation), soc (society), sci (science) etc.
Users can post to existing newsgroups, respond to previous posts, and create new newsgroups.