Six major camps were designed and built for the sole purpose of killing.  These were: Auschwitz-Birkenau, Belzec, Chelmno, Majdanek, Sobibor, and Treblinka.

Extermination camps were the facilities constructed by Nazi Germany in World War II where the Nazis systematically killed millions of Jews as part of what was later deemed The HolocaustDoris Bergen, http://www.pbs.org/auschwitz/40-45/background/ideology.html Germany and the Camp System, part of Auschwitz: Inside the Nazi State, Community Television of Southern California, 2004-2005. Bodies of those killed by the Nazis were usually either cremated or buried in mass graves. Members of other groups whom the Nazis wished to exterminate, such as Roma (Gypsies), Serbs (exterminated as a main target of Croatian Ustaše), Soviet prisoners of war, Poles, Communists, Jehovah's Witnesses, and homosexuals among others, were also killed in these camps.Philip Rosen, http://muweb.millersville.edu/~holo-con/Rosen-1999.html Beyond Anne Frank, Millersville University Annual Holocaust Conference Program, Spring 1999.