What is "bumping" a topic?

One bumps a topic when one posts a message without any real content (usually just the word "BUMP!" or "Anybody?"), just to have the topic resurface and become the top one on the list. Usually this is done to draw attention to that topic, or to try to elicit a response to an unanswered question. This should be done sparingly, and with due care. Avoid doing it as much as posssible. And welcome to MSFN!

Thanks for the welcome and the answer. I think I understand. If I'd posted a question and wanted to "bump" it to the head of the line I'd add a reply to the post that didn't add any new thoughts or info to my question. This should not be done frequently or without reason but it would be ok etiquette-wise if I had a post that no one replied to within the usual reply time for this forum and I wanted to retry getting a response.
I also should have posted my question on forum rules under Miscellaneous>Site & Forum Issues> Forum Rules I see.

Well, it's complicated... but you've got the gist of it. Let me tell you some more: to some among us, any instance of replying to one's self (instead of editing one's last post to add content) constitutes bumping. To others, me included, bumping only occurs when the reply to one's self has no new content (or no content whatever), while replying to one's own posts is not bumping when used to add new content, particularly in the case one wishes to avoid overlong posts, or to divide different (but related) subjects (as totally unrelated subjects warrant different threads, however). Nonetheless it *is* controversial, and with no consensus in sight, so it should be avoided, as much as possible, but not at all costs. Very rarely, when one has a really long winded text to post, one might even post two or three posts in succession, containing, each, a part of the main post (and this cannot possibly be said to bump the thread because it'll already be at the top, after the first post). After being here for some time, you surely will find examples of all these cases. In any case, the more usual procedure would be to edit one's last post to add new content, as much as one wants (until someone else actualy replies to it), so that the thread doesn't go to the top again too soon.

OK, think I understand better. If I post a new question and later think of something I've left out, the polite way to add it to my post is to edit rather than to reply. Glad I asked and you expounded. I'm exactly the type to forget there's an edit option and head for the quick reply button.
Re the need or not-need to bump one's post - since people get busy, sick, take vacations etc and attendance at the forum must vary, with people w/ different expertise available at different times, is there some ballpark figure where one can assume one's post has gotten lost? Re-posting the same question seems to be no-no, so bumping would be better?
All my posts have been replied to promptly so I may be asking about a non-problem.

Yes, precisely!
Well... Never bump before a day is elapsed. And in case your post is totally ignored and falls all the way to page 2, that would be the point to bump it, or forget about it. Those are extremes. Things in-between must be decided on a case-by-case, but three to four bumps in a week, if you don't do it every time you post something, would be quite acceptable.
It's definitely better to bump, in this case. Or even to ask a mod to move it somewhere better in the reply, instead of posting just "bump".
Let's hope so. It depends on the question. When one asks a truly unanswerable question (yes: they do exist!), no amount of bumping will ever get it answered.

There's a lot of debate about bumping. I, for one, detest people who bump threads. We all get a chance to see everyone's threads and if people who see the thread feel inclined to reply, they do. Bumping often does not change that.

Thanks dencorso.

Thanks jcarle for your POV.