What it's for
Port 119 is the default port for NNTP (Network News Transfer Protocol), the protocol behind Usenet — one of the internet's oldest distributed discussion systems, predating the web. Clients connect to a news server on port 119 to read and post messages in newsgroups, and servers themselves use NNTP to propagate articles to one another across the Usenet network.
Protocol basics
NNTP runs over TCP, since reliable delivery matters for both reading articles and the server-to-server propagation that keeps newsgroups synchronized across providers worldwide. The protocol supports both a "reader" mode (a client browsing and posting to groups) and a "transit" mode (servers exchanging new articles with peers). While Usenet's mainstream popularity has faded since the rise of the web and social media, NNTP still sees active use for certain technical discussion archives and specialized binary-file distribution communities.