Usenet is one of the oldest computer network communications systems still in widespread use. It was established in 1980 following experiments the previous year, over a decade before the World Wide Web was introduced and the general public was admitted to the Internet.

The articles that users post to Usenet are organized into topical categories called newsgroups, which are themselves logically organized into hierarchies of subjects. For instance, comp.os.linux.advocacy and comp.os.linux.misc are within the comp.os.linux hierarchy. When a user subscribes to a newsgroup, the news client software keeps track of which articles that user has read.

In most newsgroups, the majority of the articles are responses to some other article. The set of articles which can be traced to one single non-reply article is called a thread. Most modern newsreaders display the articles arranged into threads and subtreads, making it easy to follow a single discussion in a high-volume newsgroup.

Legal note: this article’s contents has been directly copied from a Wikipedia article called Usenet. Read more about this technology there.