USENET is a worldwide distributed internet discussion system developed from a general purpose dial-up network architecture. The idea was reportedly conceived in 1979 and put into operation in 1980 by two Duke University graduate students. USENET could be considered as a sort of hybrid between an email format and a web forum format with discussions being threaded even though posts are stored on the server in the order received regardless of which discussion it belongs to.
The main difference between a BBS or web forum and USENET is that in the former formats, messages are stored on one computer in one location. USENET is decentralized by being distributed among a large and constantly changing group of servers that each store and forward messages to one another. They do this in what are known as news feeds. Each individual user may read messages from a local server as well as post messages to the local server being operated by a USENET provider, or their internet service provider, a university or even their own web server.