A bump can be used in lots of ways. In group posts it moves posts to the top of the forum since you see the posts listed by most recent activity. That can be as has been said because the person doesn't have an answer but want to help get one, it could also be a show of support for a post or it could be used to check back later on a fast moving thread as it will now show up in your MY replies link under the groups tab or in the blue group info box to the right.
In this section, on the main answers page the questions can be sorted by latest questions, or by the amount of bumps a questions has received. Plus in this section you can get points for a bumped question.
Answer by Liansmommie at 7:27 PM on Aug. 1, 2010
Answer by FXmomTo3 at 7:20 AM on Aug. 1, 2010
Answer by AtHomeMommy-3 at 8:37 AM on Aug. 1, 2010
Answer by HotMama330 at 11:14 AM on Aug. 1, 2010
Answer by Liansmommie at 7:28 PM on Aug. 1, 2010