According to Osho, a masochist is one who asks to be hurt: 'Beat me, whip me, put me in chains,' deriving gratification from suffering. A sadist is one who enjoys the other's suffering by refusing even that request: 'No, I won't.' Both expose a perverse dance of pain and power, two sides of the same neurosis.
A masochist wants to be hurt, while a sadist enjoys your hurt and may even refuse you to make it worse.