In this respect, I'll stick solely to the Oxford English definition.

http://oxforddictionaries.com/definition/sadism

I'm a sadist, very much so. I like to take things to extremes, a lot. But to say it doesn't belong in the BDSM world....I would have snorted at that definition and carried on looking around. The only time I would absolutely 100% say that sadism has no place in BDSM is when it's exercised with no control.

Examples, I guess. My kitten isn't a masochist, at all. But I'll still take a cane to him when we play. Because I enjoy hearing his whimpers, and on good days I enjoy seeing him tear up a little. His pain threshold isn't high, so it doesn't take much. But I'm always looking for that boundary, where it's too much, and to go further would cause him serious damage. And then I look after him. I'm still deriving a great deal of pleasure from his pain, but I'm not taking it beyond reasonable limitations.

On the other hand, when I first started out I made the mistake of playing with strangers, and drew the short straw when a guy turned out to be a sadist without that control. He bust up my cheekbone, my jaw, dislocated my hips and fractured three vertebrae in my spine. I learned my lesson big time that day, and I still cope with the consequences of foolish actions.

There's a fine line between sadism and abuse. Self control makes the person. When I say "I take things to extremes", a lot of people jump to crazy conclusions of vicious and violent practices. I had one person ask me whether I really used katanas in foreplay once o_O. But it's not my extremes I'm taking things to, it's my partner's.