noun
anonymous textboard; anonymous message board
An Internet forum where users can post without revealing their identity; common in Japanese online culture.
匿名掲示板に書き込むときは、個人情報を載せないように注意してください。
When posting on an anonymous textboard, be careful not to include personal information.
掲示板 is a general bulletin board (physical or online), while 匿名掲示板 specifically allows anonymous posting.
Compound of 匿名 (とくめい, 'anonymous') and 掲示板 (けいじばん, 'bulletin board').