Question

b = tt d what it mean??

Answer 1

Bump to Top. BTT simply adds a posting to a forum thread to show activity, thereby moving it to the top of the list of threads in that forum.For instance, if a discussion thread has been inactive for a week, it can get moved down in the list or onto subsequent pages. Any activity in the thread will move it back to the top of the list. 

Posters may just want to do that and will post a BTT