olemus
Wiktionary:
1. a board on which messages may be posted, especially one in a public space
2. (computing) a system in which users may send, read and reply to public messages; an electronic message board or forum

(a) kork- või magnettahvel teadete paigutamiseks
https://duckduckgo.com/?q=office+bulletin+board&t=h_&iar=images&iax=images&ia=images

https://en.wikipedia.org/wiki/Bulletin_board

(b) liik võrgufoorumeid,
füüsilise teatetahvli elektrooniline analoog
https://en.wikipedia.org/wiki/Bulletin_board_system

https://thenewstack.io/bulletin-board-systems-social-media-internet/

https://paleotronic.com/2019/09/04/bbses-partying-online-like-its-1989/

http://www.bbscorner.com/

https://www.telnetbbsguide.com/

https://en.wikipedia.org/wiki/List_of_bulletin_board_systems