A bulletin board system or BBS (also called Computer Bulletin Board Service, CBBS) is a computer server running software that allows users to connect to the system using a terminal program. Once logged in, the user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging messages with other users through email, public message boards, and sometimes via direct chatting.
Many BBSes also offer online games in which users can compete with each other, and BBSes with multiple phone lines often provide chat rooms, allowing users to interact with each other. Bulletin board systems were in many ways a precursor to the modern form of the World Wide Web, social networks, and other aspects of the Internet. Low-cost, high-performance modems drove the use of online services and BBSes through the early 1990s.
Infoworld estimated that there were 60,000 BBSes serving 17 million users in the United States alone in 1994, a collective market much larger than major online services such as CompuServe.
For more information on this, please visit the wikipedia entry for Bulletin Board systems https://en.wikipedia.org/wiki/Bulletin_board_system