Usenet (also know as "Netnews" ) is a set of protocols for generating, storing and retrieving news "articles" (which resemble mail messages) and for exchanging them amongst a readership which is potentially widely distributed. It is organized around a newsgroup, with the expectation that each reader will be able to see all articles posted to each newsgroup in which they participates. These protocols most commonly use a flooding algorithm which propagates copies throughout a network of participating servers. Typically, only one copy is stored per server, and each server makes it available on demand to readers able to access that server.
Articles are passed between news servers using the NNTP protocol or (less often these days) UUCP.
Early versions of Usenet used B-News and then later C-News. In the mid-1990's, INN was developed to take advantage of the way the Internet worked versus the store-and-forward manner of Usenet. Since that time INN develpoment has continued and other news server software has also been developed.