That depends on the massacre.

The term "The Holocaust" in its most common usage in popular culture and academia is generally understood and defined as the systematic, bureaucratic, state-sponsored persecution and murder of six million Jews and up to half a million Roma, Sinti, and other groups persecuted as "gypsies" by the Nazi regime and its collaborators. During the time of the Holocaust the Nazis also targeted other groups on grounds of their perceived "inferiority", such as the disabled and Slavs, and on grounds of their religion, ideology or behavior among them Communists, Socialists, Jehovah's Witnesses and homosexuals.

The focus of this definition on Jews and more recently so-called gypsies as well as the common association of the term Holocaust with the murder of six million Jews in Europe results from the difference in persecutorial practice and the totality of the planned annihilation of the Jews by the Nazis.

It was the Nazis' plan and policy to kill every Jew and every "gypsy" they could get their hands on, regardless of who they were, what they did, their gender, age, nationality, class or political conviction. They built an entire administration, bureaucracy, and infrastructure to that specific end and used all the tools the modern state has at its disposal from the rail way to the army in order to achieve this goal. What the Nazis referred to as the "final solution to the Jewish question" was genocide in its most encompassing and most extreme form.

The Nazi regime subjected millions of people to violence, starvation, exploitation of labor, imprisonment, and murder but no other group was targeted so systematically and with such totality than the Jews and "gypsies". These key differences become apparent when we look at how this was put in practice. While the Nazis did indeed start killing handicapped and disabled Germans before they started killing Jews, they did not pressure foreign governments to hand over their handicapped for example as they did with Jews. The fact that the Nazi government exerted diplomatic pressure on the Imperial Japanese government to hand over the 18.000 Jews in Shanghai demonstrates that for the Nazis even a comparatively small number of Jews thousands of miles away from any of their territory represented such a danger to them in their minds that they had to die.

Similarly, the Nazi regime imprisoned and shot thousands upon thousands of Soviet and Polish citizens, yet they never built camps that only existed with the sole purpose of murdering all Poles or Soviets they could get their hands on like they did with Jews. Camps such as Sobibor, Treblinka and Belzec were nothing but a modicum of infrastructure surrounding a gas chamber. In Treblinka, a camp rather small when compared to, say, Auschwitz, up to 900.000 Jews were murdered in the span of a year.

This all does in no way minimize or trivialize the horrors and cruelty of how the Nazis treated their non-Jewish victims. Soviets and Poles, handicapped and mentally ill people, Communists and Socialists, Jehovah's Witnesses and homosexuals, all suffered tremendously under the Nazis and unimaginable numbers of them were killed. They all need to be remembered.

Yet, when we describe what the Nazis termed the "final solution" some structural and ideological differences become apparent. I have previously mentioned death camps and diplomatic pressure but another example would be that the Nazis indeed did try to kill every Jew, including babies and children. Even within the gruesome and savage history of Nazi atrocities against so many people, the description of SS troops invading a hospital and killing Jewish babies by smashing their heads against walls or setting up a whole state apparatus concerned with the systematic gassing and shooting of men, women, children, and the elderly evokes a special kind of terror and revulsion.

The term Holocaust is in the historical field first and foremost intended as a term that acknowledges and contains the description of this difference, without attempting to moralize this difference or make any sort of statement, which was "worse", because when you deal in the category of Nazi atrocities against all its victims "worse" is not really a category that can cover it anymore.

While more can be said on how the term became so ingrained in popular memory, the Wehrmacht massacres in the Soviet Union show the fluidity of the term in this case. Because while the Nazis didn't institute a policy to kill all Soviets everywhere, the massive massacres committed against the population of the USSR and the Holocaust were ideological related as they were both understood within a framework of "the fight to death against Bolshevism", which was so central to the Nazi ideology. Jews were viewed as the plotters and planners behind the ideology of Bolshevism itself and therefore the Holocaust really only started with the invasion of the Soviet Union.

In preparation for this invasion, the German political and military leadership had drawn up plans for what they called a war of annihilation. The goal was not just to bring the Soviet Union to its knees politically and militarily but to destroy what they perceived as the very basis of Bolshevism: Jews and Bolsheviks. The Soviet Union should not just be conquered but rather, the base and idea of Bolshevism was to be completely destroyed and with it, all it proponents.

The Nazis had this deeply held believe that Jews were responsible for Bolshevism thus when planning the invasion, they drew up documents that not only stipulated that no member of any German formation could be tried for war crimes committed in the Soviet Union but also that every "proponent of Bolshevism" they came across – party members, political commissars, Jews – should be killed immediately by the Einsatzgruppen – units composed by members of the SS, the Gestapo, and others – or other formations such as the Wehrmacht.

And so, the killing of the Soviet Jews was nothing less than central to the Holocaust while the totality of Soviet victims (including Jews) are usually understood under the "war of annihilation" metric.