On forums and message boards where the most recently replied-to threads move to the top of the page, a TTT, or To The Top, post is for what it says, moving a post to the top of the page, where it will get attention, and hopefully replies. The creator of a post seeking someone (or something) will often sit and refresh the forum page, TTTing his post when he fears that nobody will notice it.

In some forums, TTT is replaced with "bump." No studies have been formed to assess why this occurs in some forums and not in others.

I'm surprised this one isn't in the Jargon File already, but perhaps a newer edition has it. Oh, and as someone else has softlinked, TTT is also the standard abbreviation for The Two Towers.