Scouter194 asked on a thread what a "bump" is.
If someone posts with "bump" as the text, it generally means they have no answer or specific comment, but want to push your post back up to the top of this list in hopes that someone else might. Sometimes we know there is a member who might be of help, but that they don't log on often. As well, in this day of small devices, what is on the first page may be far out of sight once off the first few lines, or at least it seems so (I use a laptop only, finding the small screens on a "smartphone" to be less than useless).
For posts such as the Wednesday night chat reminder, it is just to keep it at the top of the list.