The Nazi Holocaust was such a major event in history that the word 'holocaust', which means catastrophe or destruction in Yiddish and Hebrew, often only refers to this particular event. Rarely is the word used for other events or situations that could be applicable because it has such a strong tie to the genocide of more than 11 million people during Hitler's rule of Germany and World War II.
The Nazi Holocaust started when Hitler was named chancellor of Germany. Shortly thereafter, he implemented a totalitarian government and became dictator, with his Nazi leaders working to help build the army and advance the Nazi agenda on a political front. The entire event started simply enough with the Nuremburg Laws, which essentially stripped Jews of their rights as equal citizens and boycotted their businesses. Eventually, they were forced from their businesses and their homes, into ghettos where they would live in squalor with other 'inferiors'. They were forced into labor when they could be, starved and exposed to disease, and many died merely as a result of illness or exposure at this period in time.
As the Holocaust gained power, it became apparent that there was a need for more organization. Germany was taking over increasing numbers of countries and they needed a system for dealing with all of their prisoners and inferiors that were being captured or kept against their will in some form. As such, they developed camps to help hold the inferiors and prisoners of war. Most people think of concentration camps when they hear about the Holocaust, but there were also labor camps, transit camps, prisoner of war camps, and extermination camps. Each had its own purpose and was used for a certain group of people.
As a result of the Nazi Holocaust, more than 6 million Jews were killed at the hands of the Germans, with another 5 million or more people killed, as well. Discrimination included Romani, Soviets, Polish citizens, homosexuals, disabled people, political opponents, Jehovah's Witnesses, and other people who did not fit the Nazi ideology for the Master Race. These people were killed by many methods, including starvation, exposure, medical experimentation, torture, and outright murder in some cases. Once the camps were set up, mass killings were common place, involving execution-style shootings or trips to the gas chambers, which prisoners were usually told were "showers".
This historic event involved the largest case of genocide in the 20th century. There were some survivors, including a few who are still alive, and even some who have shared their stories.