In online lingo, "bumping" refers to posting in a thread on a message board solely to move the thread to the top of the forum. Bumping increases the thread's visibility, but because a bump doesn't contribute anything new, many communities view it as a type of spam.
How to Bump a Post
Most message boards sort threads chronologically by their most recent replies, so whichever thread has the newest reply shows up on top. Any new post in a thread bumps it to the top, at least until another thread receives a reply. Bumping takes advantage of this design. Even a single word reply -- often the word "bump" itself, but any word works -- sends the thread to the top of the page.
Many forums frown on -- or explicitly forbid -- bumping posts. When a thread moves to the top of the board, it leads users to believe that the thread has new content. Bumping your own thread to get more attention comes across as spamming. Bumping another user's thread isn't much better, as it adds nothing of value. For example, rather than bump another person's post because you have the same question, add your own angle or share what you've already tried to solve the problem.
Posting meaningful content isn't always enough to satisfy forum etiquette. A related faux pas, "necroposting," involves posting on an old thread. When you reply to a thread that hasn't had any activity in months or years, you bump it to the top of the board, reviving the dead discussion. Because old threads often have outdated information or are written by long-departed users, many message boards prohibit necroposting. Some automatically lock old threads to prevent it from happening. Rather than reply to a thread with no activity in the last month, start a new post. Link to the old thread, if necessary, to include it in the conversation.