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.

Usenet is older than the internet itself. Originally set up to allow academics and others in specialized fields to engage in group discussions with their peers across the globe, it has since evolved into an uncensored system of exchanging virtually anything that can be transmitted between computers.

Usenet functions a lot like email. Except that instead of addressing messages to an individual, they are addressed to a group. And anyone wishing to read or post messages in a particular group, does so by connecting to a Usenet Server across an internet connection. A newsreader (ie.Outlook Express) is needed on the user’s computer to read articles and download attached files. You “subscribe” to a group by telling the software in your own computer to check the messages in a particular group. (Don’t be frightened by the term “subscribe.” Nowhere is there ever a subscriber list. The term “subscribe” is used in reference to how you set up your computer and software. Only you and your computer know which groups you have “subscribe” to.) 

There is no “central” Usenet Server. Rather there are thousands of Servers chained and crosslinked together in order to exchange articles between them, and to keep the articles available for their own users to read for a period of time ranging from hours to weeks. (It is this lack of centralization that has protected Usenet from the legal attacks such as that which destroyed Napster.)