What was the systematic and purposeful destruction of a racial, political, religious, or cultural group called during World War II?

The systematic and purposeful destruction of a racial, political, religious, or cultural group during World War II is best described as genocide. This term specifically refers to acts that are intended to destroy, in whole or in part, a national, ethnical, racial, or religious group. During World War II, the term came to prominence largely due to the atrocities committed against the Jewish people by the Nazis, which is what is commonly referred to as the Holocaust. The Holocaust is indeed a specific instance of genocide; however, genocide as a concept encompasses a broader range of actions against various groups throughout history, not just those conducted during the Holocaust.

The Nuremberg trials, while important, were legal proceedings held after the war to address war crimes committed by Nazi leaders, rather than being a term that defines the act of systematic destruction itself. Similarly, "war crimes" refers to violations of the laws of war and does not specifically denote the targeted extermination of cultural or ethnic groups. Therefore, the term genocide adequately captures the general nature of such acts during that period, making it the correct answer.