I'm probably the only person that does not know this but...?
457988
Good question, actually.  As others have said, it stands for sado-masochism.  The "sado" part comes from sadist, which was derived from the Marquis de Sade.  The term "masochism" was coined by the 19th century psychiatrist Krafft-Ebing based on Sacher-Masoch's writings (Sacher-Masoch was not pleased with this).  To simplify it: a sadist enjoys inflicting pain (or humiliation, etc.), and a masochist enjoys receiving it.
264178
I'd like to answer but I don't understand anything...\nGoo afternoo to you too!
43229
i know the answer but did not know the answer.
1132044
I've never heard of that....
356665
Nope, wow I haven't realy heard of it.....
987341
i know. i learned about that, i forgot what it's called.
586320
Yes I read the details, but by the looks of these answers, no one else does!
124588
i even haven't heard of it \ni just wanted to leave an answer\nwait for anybody else's answer\nthere must be someone
242088
Is this a question??\nI haven't heard this.
551134
who the hell knows???? If you figure it out let me know!!!!
668272
no i didn't know that.thank
683906
well thanks for telling me i didn't know
994499
Where did you learn this from?  I've never heard of it.
455098
what?i never heard this.
1044668
HUH???? i'm clueless.
587493
i have no idea abt it.
87638
No one knows the answer I would guess, but it looks like you have 1 answer.