These are groups of people who discuss a multitude of subjects of their interest online. Their comments are recorded on the discussion website for all members of the discussion group to see and read. There are a number of different terms that refer to essentially the same concept as discussion groups and those terms are listed below.
There are aggregations of discussion groups, such as Yahoo Groups, Google groups, AOL groups, Delta Groups, Facebook Groups, LinkedIn Groups, and groups within many websites who discuss the subject matter of the website.
Discussion Groups are of great value, because they are "Primary Sources" of information and a way of identifying and extracting a ideas, thoughts, and experiences of interest that would never be available by any other means, such as published articles, books, etc.
It is similar in some ways to the pre-Internet days, when people would write Letters To The Editor (LTTE). But these were few and far between, and would usually involve people who felt strongly about a given subject, and who had the extra motivation to look up the mail address of the editor, a chore in itself, then write the letter, put it in an envelope, attach the stamp or go to the post office to get a stamp, and mail the letter. These "chores" and expenses of time and money added to the inhibition to write letters to the editor, and although a relatively few LTTEs were ever written, compared to the people who felt an internal response to something they read, even fewer of the LTTEs were ever published.
Now, however, people can respond immediately to any suggested idea, subject, event, experience, etc., and have their thought and expression available to the world instantly, at little or no cost. This has resulted in billions of messages being posted by people on subjects of their interest who would never have sent LTTEs, and therefore add information, thoughts, and ideas that would never be known.
Actually, discussion groups are really only a subset of online sources for postings of comments, since newspapers, periodicals, blogs, and numerous other sources online have spaces for comments too, and these are all "Primary Sources" as well.
Terms for discussion groups and related types of groups: Discussion groups, News groups, Usenet newsgroup, Bulletin Board System (BBS) , Virtual communities, mailing lists, electronic mailing lists, forum, Internet forum, message boards, bulletin boards, "Boards", discussion forum, online bulletin boards, and other similar terms. But they all refer to online groups of people interested in a particular subject or topic.
Other important names and terms related to discussion groups:
Usenet: https://en.wikipedia.org/wiki/Usenet
DejaNews: Prior to the acquisition of its archive by Google in 2001, the Deja News Research Service was an archive of messages posted to Usenet discussion groups, started in March 1995.
NewsDemon, America's number one UseNet provider: http://www.newsdemon.com/
Usenet.com: Provides reviews of the top Usenet Providers;
Virtual Communities:
Virtual Communities include a number of different online website types, including social networks, discussion groups, etc.
Wikipedia List of Virtual Communities with more than 1 million members or users:
http://en.wikipedia.org/wiki/List_of_virtual_communities_with_more_than_1_million_users
Wikipedia List of Virtual Communities with more than 100 million members or users:
http://en.wikipedia.org/wiki/List_of_virtual_communities_with_more_than_100_million_active_users
Wikipedia List of Social Networking Websites:
http://en.wikipedia.org/wiki/List_of_social_networking_websites