If you're asking this you're a creep.
genocide
mass murder
It is considered to be genocide as soon as mass killing becomes directed at a certain ethnic group.
The word you're looking for is "genocide."
mass murder
mass-murder
The holocaust was when Hitler tried to eliminate the Jews by mass murder and genocide. The cause was antisemitism turned evil.
Genocide is mass murder against a certain culture, such as the Nazi's exterminating Jews, homosexuals, communists, the disabled, black people, etc.
genocide
well genocide is the mass murder of a single race
Catastrophic extinction event.
"Genocide" is a term which means a mass killing of a particular group, such as Jews. In a sentence : "Hitler performed mass Genocide during WW2 on Jews" Source : http://www.Google.co.UK/search?sourceid=chrome&ie=UTF-8&q=define:genocide and such as the Armenian genocide when the Turkish killed one and half million armenians at 1915.