Before the uptake of the World Wide Web, Usenet newsgroups were among the most popular Internet services, and have retained their noncommercial nature in contrast to the increasingly ad-laden web. In recent years, this form of open discussion on the Internet has lost considerable ground to individually-operated browser-accessible forums and big media social networks such as Facebook and Twitter.
Google Groups offers at least two kinds of discussion group; in both cases users can participate in threaded conversations, either through a web interface or by e-mail. The first kind are forums specific to Google Groups which are inaccessible by NNTP and act more like mailing lists. The second kind are Usenet groups, for which Google Groups acts as gateway and unofficial archive (the Google Groups archive of Usenet newsgroup postings dates back to 1981). Through the Google Groups user interface, users can read and post to Usenet groups.
See also my Quora answer to: