bulletin board

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A board on which notices are posted.
• noun Computers A system that enables users to send or read electronic messages, files, and other data that are of general interest and addressed to no particular person.

from The Century Dictionary.

• noun A board publicly exposed, on which to placard recent news, notices, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a board on which messages may be posted, especially one in a public space
• noun computing a system in which users may send, read and reply to messages of interest to no particular person; an electronic bulletin board

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a board that hangs on a wall; displays announcements
• noun a computer that is running software that allows users to leave messages and access information of general interest