Usenet is a HUGE messageboard, consisting of different messageboard topics (newsgroups), which is actually a network of servers that all share more or less the same content locally so users can access it faster, some people just happen to use it for warez and files and whatever (since you can encode a file into a text-string and post it up, usually in multiple parts). Most ISPs have usenet servers setup for local user use, but they often have the binary (file) newsgroups disabled.