A newsreader is an application program that reads articles on Usenet (a distributed discussion system, which groups its content into a hierarchy of subject-related newsgroups, each of which contains multiple threads or discussions). Newsreaders act as clients which connect to a news server, via the Network News Transfer Protocol (NNTP), to download articles and post new articles. In addition to text-based articles, Usenet is increasingly used to distribute binary files, generally in dedicated "binaries" newsgroups.