Forums have a specific set of jargon associated with them; example: a single conversation is called a "thread", or topic.
A discussion forum is hierarchical or tree-like in structure: a forum can contain a number of subforums, each of which may have several topics. Within a forum's topic, each new discussion started is called a thread, and can be replied to by as many people as so wish.
Depending on the forum's settings, users can be anonymous or have to register with the forum and then subsequently log in in order to post messages. On most forums, users do not have to log in to read existing messages.
The modern forum originated from bulletin boards, and so-called computer conferencing systems, and are a technological evolution of the dialup bulletin board system. From a technological standpoint, forums or boards are web applications managing user-generated content.
Early Internet forums could be described as a web version of an electronic mailing list or newsgroup (such as exist on Usenet); allowing people to post messages and comment on other messages. Later developments emulated the different newsgroups or individual lists, providing more than one forum, dedicated to a particular topic.