According to the United Nations, the definition of genocide is:
"any of the following acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such:
a. killing members of the group;
b. causing serious bodily or mental harm to members of the group;
c. deliberately inflicting on the group conditions of life calculated to bring about its physical destruction in whole or in part;
d. imposing measures intended to prevent births within the group;
e. forcibly transferring children of the group to another group."
In modern society, genocide has come to apply to any planned mass slaughtering of a particular group of people, and to a lesser extent, any disaster that was brought about by artificial or human means and produced a large number of casualties. It's suffered the usual media sensationalism and over the years has lost much of its meaning. In the eyes of society these days, genocide is no longer the profound offense to all of civilization that it was taken to be in 1945, but just an obscure problem in an equally obscure nation by an equally obscure dictator.
The Nazis attempted to conduct a genocide during World War II.