Bulletin Board System
Bulletin Board System (also known as BBS) is most commonly used when referring to Citadels but can refer to any message board.
The BBS, from the user's perspective, is segmented into "rooms", each of which is dedicated to a topic. Within each room are a series of posts, marked with date-time stamp from individual users. The user reads all the posts, posts his/her own reply or message, and moves onto the next room.
In this manner the message board emulates a "bulletin board", such as roommates in a large house might use to communicate with each other. Entirely text-based (at least in dial-up format), the BBS was the primitive forerunner to the modern thread-based forum.