BDSM is a convenient abbreviation for most of the interesting activities discussed in alt.sex.bondage.
Its so convenient that it packs six intials into four letters B&D/D&S/S&M=>BDSM. Its generally understood to include related activities/phenomena that dont fitstrictly into any of those three catagories. An ''umbrella term'' like this is useful because so few actual (as oppesed to theoretical) activities fir into only one catagory.
Bondage
Bondage deals wiith tying people up (or being tied). Or chaining them up, or restraining them with straps, or straight jakets, or.....well, you get the idea, no? In theory it can be enjoyed simply for its own sake--the sensations and images of it. In fact, some people do enjoy bondage as bondage, without any interest in D&S or S&M, but far more people find it pushes thier D&S button at the same time, or use it only for the D&S aspect, or combine it with D&S and /or S&M.
Dominace and Submission
D&S deals with exchange of power, trust, obedience, role-play. ''slavery''...one person submitting to the commands os another. Like bondage, it can exist as a seperate phenomenon, but it's likley to incorporate the others. Bondage may be used to enhance the feeling of submission. Pain-play (i.e S&M) may be used to emphasize the position the submissive is in or as punishments for disobedience.
S&M
S&M sort of stands for ''sadism and masochism'' but not quite the same way the psychiatric establishment uses those terms. So its less cinfusing to keep the phrase tidily together as S&M. S&M involve strong
sesations. Its associated with pain, in particular, in most people's minds, but in fact pain is only one class of sensations used. Futhermore, some stimuli which would ordinaly be percieved as pain by some partipants when in a S&M headspace!
(Note that i said some) While I dont have statistics on this, its my empression that S&M is the one phenomeon of these most likely to occur without the others. Nonetheless, it is quite common for one'sintrest in S&M to be in the context of bondage or D&S ( the pain makes it so very much cleare that one cant get away because one is tied up, for example) or simply alongside an interst in bondage and/or D&S.
Interstingly, while most 'vanilla' (i.e not-into-BDSM) people do not consider tickling to be a BDSM activity many BDSM folks do.
More termiology
Some people like to be tied up, whip people, or give orders. Others like to be tied up, like to be spanked or whipped or like to obey. Because so many of the words one might use to describe these preferences seem specific to just one aspect of BDSM, push people's buttons, or only fit the ways some people play, folks in the scene use the generic terms 'top' and 'bottom' (Note that these words have different meanings in gay male culture, if not im mistaken)
In bondage, a top like to tie up bottoms, In S&M a top likes to provide strong stimulation (pain or otherwise) to a bottom. In D&S a top orders or controls a bottom. A 'Switch" is someone who enjoys being top and bottom.
Note that its not always the top who's in control of things--in fact, much less often than the other way around! For example, a bottom might ask to be tied and his.her top might decide to honour that request, asking the bottom if there were any particular things he/she wanted the top to do to him/her. Also many people use ''safewords'', coded phrase that means ''Im not playing'' ''I really need to stop'' If a couple uses a safeword, the bottom can stop the activity by using the ''safeword''
Some people claim that the bottom is always the one who's really in control, no matter how things look. They're mostly right, but things can get more complicated.