A discussion group is an online forum for individuals to discuss various topics amongst each other. People add their comments by posting a block of text to the group. Others can then comment and respond. In the early days of the Internet, USENET was the most popular type of discussion group, but now discussions mostly take place over the World Wide Web using special server software. The term discussion group encompasses bulletin boards, listservs, mailing lists, and newsgroups.

Discussion groups differ from chatrooms and instant messaging because they usually deal with one topic and personal exchanges are typically discouraged. Discussion groups are often archived. These archives may be organized by thread, which means all the messages that reply to a starting message can be read in some order. Participants in discussion groups should realize that what they have to say will be public knowledge for years to come. For example, Google's Groups (formerly DejaNews) is an archive of Usenet articles dating back to 1981. Discussion group archives are sometimes the best way to find an answer to very obscure questions, such as how to fix a particular computer problem.