Sadism

Sadism is a condition in which people get pleasure from humiliating, harming or hurting others. Often the pleasure is of a sexual kind. When a person finds pleasure in being hurt or humiliated, their condition is called Masochism.
The terms "sadism" and "masochism" were both invented by Richard von Krafft-Ebing, a German psychiatrist. He named Sadism after the Marquis de Sade, a French nobleman who in the eighteenth century wrote many books, stories and plays. Sade's books include many characters who find pleasure in cruelty, including torture and even murder.
These kind of people usually enjoy when others are hurt, but specific ones love pain in general. Most of the time people who are masochistic or sadistic are sad in real life.
The condition is often fetishized on the internet and sometimes related to self-doubt or self-hate.
Different forms of Sadism.
At first Sadism meant only cruelty for sexual pleasure, but as the word became more widely used its meaning changed. Nowadays any person who enjoys being cruel to others can be called "sadistic," even if they get no sexual excitement from what they do.
Some people who have sadistic sexual fantasies mean no real harm to anyone. In BDSM a "top" or dominant person will bind his or her partner or "punish" them in different ways, but what they do will not go beyond limits which the partner has agreed on. On the other hand, a small minority are severely perverted or mentally ill, and wish to act out their sadistic fantasies for real. Such people are rare, but they can be very dangerous. Many serial killers and psychopaths have been sexual sadists.
Treating sadism.
Treating sadism is difficult, but it looks like psychotherapy can help in certain cases. Note: It has not been proven that people with sadism can be successfully treated. The former statement is not accurate.