1.
message board; bulletin board
A board where messages can be left for others. Originally referred to physical boards at train stations or public places. Now also used for online message boards and forums.
Usage
Historically, 伝言板 referred to chalkboards at Japanese train stations where people could leave messages before mobile phones. These have largely disappeared. The word is now commonly used for online message boards and the NTT disaster message service (災害用伝言板).