Bulletin boards, also called newsgroups or discussion groups work in a similar way to electronic mail. Instead of writing messages to individual users, participants in bulletin boards post their messages on a news server. The messages are stored on the news server in a hierarchical directories. Users participate in bulletin boards by reading the messages and responding to them.
From : www.walsalleducation.org/wegfl/about_grid/content_help/faq.cfm