Usenet is a set of internet discussion groups, which use a protocol separate from the World Wide Web. Usenet is organized by topic, with individual topics contained in "newsgroups", which are organized into hierarchies. Usenet has newsgroups about every topic imaginable. Usenet's structure is different than web-based discussion boards: messages are propagated by participating news servers, instead of using a web server.
Two Duke University graduates, Jim Ellis and Tom Truscott, established Usenet in 1980. It was called the "poor man's ARPANET." In 1987 the "Great Renaming" occurred, when the Usenet groups were reorganized and renamed into the current method of hierarchies.
Originally Usenet usage cycles were dependent upon universities, which, along with businesses and the U.S. military, supplied many users. All the newbies entered in September, acted like lamers, got slapped across the face, and wisened up. Then in 1993 AOL offered Usenet access, and newbies began coming in all the time, leading old timers to talk about the "Eternal September."
Since then World Wide Web eclipsed Usenet. Nowadays a lot of people go on Usenet to get warez and porn. Most American ISPs, like AT&T, Verizon, Comcast, etc., no longer supply Usenet access for their customers, but Usenet still thrives in Europe, and Americans can still get Usenet access via paid news servers.
On May 20, 2011, Duke University, the origin of Usenet, shut down its original Usenet server after more than 20 years.
Still up. While most ISPs have discontinued supplying Usenet access through their own servers, Google provides access through "Google Groups", or you can get a newsreader program and purchase access from a Usenet service provider, like Giganews or Altopia.