NNTP (Network News Transfer Protocol) is the protocol used by Usenet news servers and clients (readers).
Usenet is a huge shared message system which is used on the Internet.
Usenet consists of newsgroups such as comp.sys.ibm.pc.hardware.video and rec.collecting.sport.hockey.
The NNTP protocol exists on the Application Layer of the OSI Model.
NNTP utilizes TCP port 119; NNTP with SSL utilizes TCP port 563.
Popular NNTP servers include INN and Diablo.
Pan is a newsreader for the Gnome environment, which runs under Unix, Linux, Mac OS, and Microsoft Windows.
Other popular NNTP clients for Unix include rn, trn, and nn.
Xnews, NewsFlash Plus, and MesNews are NNTP news readers for Microsoft Windows.
Additional Reading on NNTP
The NNTP protocol is defined in RFC 977: Network News Transfer Protocol.