what does it do and, more importantly 
how do I do it?
It moves older threads from lower to higher in the chronological list. How do you do it? Simply by posting to a thread. However, it’s considered a mild breach of internet etiquette to do that. Please don’t get in the habit.
Or I’ll have to take your webshooters away from ya.
Actually, it’s when a stripper juts their hip out - usually followed by the ‘grind’, wherein they slowly sorta rotate their hips, so they jut out towards the floor and back again.
Or so I’ve heard 
okay, then when a poster only will have the word “bump” in their reply, it is simply to resurrect an old thread?
hmmm…(thinks to self) what is the point ?
strippers on the SDMB? point the way, please!
:: looking for stash of singles, stashed away for just such an emergency! ::
yes. There is, for example, a thread in this forum that details, step by step, how to do a variety of coding (for quotes, lists, url codes etc.) every now and then, somebody will post simply the word ‘bump’ so that the thread reappears near the ‘current page’, so folks can see that the question had been answered already instead of posting a new thread.
Generally speaking, as UncleBeer pointed out, doing a ‘bump’ is more often than not a ‘faux pas’. For example, if you’d posted a thread about ‘who’s your favorite teletubby’ and it got very little action, it’d be frowned upon to ‘bump’ it back up to the forefront.
Similarly, if there had been a particularly rankorous pit thread, debate, whatever, where folks started getting visibly angry, but it’d subsided, nobody would thank you for ‘bumping’ it.
if you’re in doubt about how the action would be recieved, of course, the best alternative would be to email a mod in that forum to ask what they thought.
"LA-LA!!!"
La-la is my favorite teletubby.
Answer to #1: Hmm… not doing anyone at the moment.
Answer to #2: Unless you’re female, it’s not going to happen!
(the handle’s an old college nickname- has nothing to do with the practice of bumping threads as described by UncleBeer)
Main Entry: 1bump
Pronunciation: 'b&mp
Function: noun
Etymology: probably imitative of the sound of a blow
Date: 1592
1 : a relatively abrupt convexity or protuberance on a surface: as a : a swelling of tissue b : a cranial protuberance
2 a : a sudden forceful blow, impact, or jolt b : DEMOTION
3 : an act of thrusting the hips forward in an erotic manner
or
Main Entry: 2bump
Date: 1611
transitive senses
1 : to strike or knock with force or violence
2 : to collide with
3 a (1) : to dislodge with a jolt (2) : to subject to a scalar change <rates being bumped up> b : to oust usually by virtue of seniority or priority <was bumped from the flight>
intransitive senses
1 : to knock against something with a forceful jolt
2 : to proceed in or as if in a series of bumps
3 : to encounter something that is an obstacle or hindrance <bumped up against a chair>
- bump into : to encounter especially by chance
I meant ‘were’ not ‘where’. Oops. :o