Just as others had explained, bumping of thread simply means raising a thread that has not been active for long. If you reply a thread that is not among the first three pages, it is called bumping, which means you wake an argument or the discussion due to some reasons which can include needing more explanation from the general public or from the OP.

Sometimes, many people don’t like bumping threads because it is been done by some users who are just willing to meet their posting requirements for their respective signature campaigns; but for Service boards, it is very important so that you will bring your thread up for business discussions.