The Holocaust was a period in history at the time of World War II; over the course of 6 years, when millions of Jews were murdered because of who they were.
The killings were organised by Germany's Nazi party, led by Adolf Hitler. Jews were the main target of the Nazis, and the greatest number of victims were Jewish.
Nearly seven out of every 10 Jews in Europe were murdered because of their identity.
The Nazis also killed other groups of people, including Roma and disabled people. They also arrested and took away the rights of other groups, like political opponents. Many of them died as a result of their treatment.
The Holocaust was an example of genocide. Genocide is deliberately killing a large group of people, usually because they are a certain nationality, race or religion.