Holocaust denial is, at its core, an antisemitic conspiracy theory.
The Holocaust was a genocide perpetrated by the Nazi regime against European Jews between 1941-1945. Six million Jews were murdered in death camps, concentration camps, ghettos, killing fields and elsewhere.
There is an ongoing effort to distort, disprove and conceal the facts of the Holocaust. There are those who simply deny the Holocaust ever happened and those who deny elements of the Holocaust, most importantly the fact that Nazis used poison gas to kill Jews in death camps. Implicitly and explicitly, Holocaust deniers argue that this entire chapter of history is an elaborate hoax by Jewish propagandists who wanted reparations from Germany, to gain world sympathy and, in turn, succeed in the creation of a Jewish state.