One of the most widely used definition of Usenet is quoted here:

"Usenet is a world-wide distributed discussion system. It consists of a set of "newsgroups" with names that are classified hierarchically by subject. "Articles" or "messages" are "posted" to these newsgroups by people on computers with the appropriate software -- these articles are then broadcast to other interconnected computer systems via a wide variety of networks. Some newsgroups are "moderated"; in these newsgroups, the articles are first sent to a moderator for approval before appearing in the newsgroup. Usenet is available on a wide variety of computer systems and networks, but the bulk of modern Usenet traffic is transported over either the Internet or UUCP. " - What is Usenet? Part 1

For a full and detailed description I strongly advise you read the following two articles in their entirety:

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

http://www.faqs.org/faqs/usenet/what-is/part2/

It is also important to know that there is a certain etiquette that should be followed when posting to a newsgroup. These guidelines are below and are a must read if you do not want to get flamed!

http://www.faqs.org/faqs/usenet/primer/part1/

http://www.faqs.org/docs/jargon/T/top-post.html

Last but not least, when using GroupBrowser.com it is important to understand these simple truths, and from this information decide whether you want to read these forums.

• No one "owns" Usenet and the information being integrated into these forums from the newsgroups are un moderated. Due to this you may find links to ads and porn, profanity, and a myriad of other objectionable material that may be posted to these newsgroups. We do implement a killfile to remove most of the spam, but GroupBrowser has no control over the content that may appear in these forums
  
  
• If you do not follow the etiquette guidelines I have posted above, you will get flamed. Please read and follow these guidelines in order to avoid embarressment.
  

Now I know that information may sound harsh and uninviting, but as you use these newsgroups you will find the wealth of knowledge available to your from peers to be incredible and you may walk away with a few new friends from other parts of the world.

Welcome to Usenet!