A running commentary of text messages pertaining to one topic or question. Message threads are used in all forms of user discussions on the Internet, including Usenet newsgroups, Web-based forums, blogs, chat rooms, groupware and e-mail.

The "thread" refers to the collection of messages organized by the software. The messages are displayed in "flat" chronological order by date of posting or in "question-answer" order. The latter is a thread of one question followed by all answers in a hierarchy. Subthreads may also be supported, which enables comments in one of the replies to start another thread that remains linked to the original. See newsgroup and forum.