interaction, especially sexual activity, in which one person enjoys inflicting physical or mental suffering on another person, who derives pleasure from experiencing pain.

What is S & M mean?

Urban Dictionary defines S&M, or Sadism and Masochism, as "The practice of using pain as a sexual stimulant." Cool.

What does it mean to be a sadist?

: one characterized by sadism : a person who takes pleasure in inflicting pain, punishment, or humiliation on others a sexual sadist He's a sadist and, where Toby is concerned, an unusually relentless one: he's in the boy's face constantly, prodding, belittling, taunting.—