Definitions for "Usenet newsgroups"
Usenet is a huge collection (several thousand) of discussion groups, called 'newsgroups', on a wide range of different topics. These groups are for public discussion; a message posted to one of them will be seen by anyone reading that group. For more information about Usenet, you can use your newsreader and read news.announce.newusers.
The individual discussion groups within USENET.
Usenet is a worldwide network of discussion threads, or series of postings, on a variety of topics. Usenet is available to most Internet users and is controlled by no single entity. Currently there are over 14,000 Usenet newsgroups. Some newsgroups are moderated (screened to ensure that the content of your message is appropriate for the group) and some are unmoderated (not screened prior to posting).