
Nazi concentration camps were death camps and forced labour camps operated by Nazi Germany during the Second World War. There were 27 main camps and at least 1,100 smaller camps in Nazi Germany and the territories it occupied.
The five Nazi death camps were Chełmno, Belzec, Sobibor, Treblinka, and Auschwitz-Birkenau. Around 2.7 million Jews were murdered in these five camps.
In other concentration camps, labor camps, and ghettos, the Nazis murdered an additional 800,000 to 1,000,000 Jews.
Half a million non-Jews were also murdered in Nazi concentration camps, including 5,000 to 10,000 LGBT people.
The camps were a key part of the Holocaust and Adolf Hitler's Final Solution.

The death camps' purpose was to mass-murder Jews as quickly and efficiently as possible (along with others who were "inferior" or "undesirable" according to the Nazis).
Gas chambers at the camps made it possible for the Nazis to kill hundreds of people at a time. Thanks to the death camps, the Nazis were able to kill people 10 times more quickly than in other genocides in history (according to a 2019 study).
In a 100-day period between August and September 1942, the Nazis killed over 1.47 million Jews, mostly at death camps. One out of every four Jews who died in all 6 years of World War II were killed during this 100-day period. In some areas, more than 99.9% of the Jewish population was murdered in camps.
Many people were killed as soon as they arrived at the death camps. Prisoners who were 'selected' to live (so they could do slave labor) were not expected to live more than a few months.
The Nazi concentration camps had other purposes too. These included:
The concentration camps were part of the Nazis' plan to kill every Jew in Europe.
The five Nazi death camps were Auschwitz-Birkenau (where over a million Jews were murdered), Chełmno, Belzec, Sobibor, and Treblinka. Almost all victims of these camps were Jews. In these five camps, the Nazis murdered around 2.7 million Jews.
The Nazis also murdered 800,000 to 1,000,000 Jews in labor camps, concentration camps, and ghettos (like the Warsaw Ghetto).

The Nazis murdered half a million non-Jews in concentration camps.
Jews were most commonly the victims of the Nazi concentration camps. However, the Nazis believed there were many other "undesirable" groups. These included (among others):

Most inmates were brought to the camps in cattle cars. When they arrived, the Nazis 'selected' which prisoners would be killed right away and which would be allowed to live (and work as slaves). Some groups were often selected for immediate execution: children, pregnant women, elderly people, people with disabilities, and anyone who looked weak or sick.
The Nazis took all of the prisoners' belongings, shaved their heads, assigned them numbers, and made them wear uniforms with badges on them.
Conditions in the camps were cruel, inhumane, and deadly. Prisoners were starved and denied water. They were worked brutally, sometimes to death. The camps were extremely overcrowded, and diseases were very common. There was no sanitation or real health care. People who could not work were killed.

The five Nazi death camps were Chełmno, Belzec, Sobibor, Treblinka, and Auschwitz-Birkenau (which included a separate women's section).
Other major concentration camps included: