"Holocaust" as normally used refers to the deliberate targeting and attempted annihilation of the Jewish people. These were the Nazis primary target.
Other "untermensch" eg gypsies were effectively "add-ons" (I know this sounds disrespectful, but they weren't the main targets).
The word itself is from a Greek term for a sacrifice in which the entire animals burned on the altar.
The disabled were killed because they gave nothing to society. Homosexuals were despised because they were unlikely to breed citizens for the Reich (another Nazi aim was for every family to have at least 4 children).
The 17,000,000 non-Jews who died were largely Slavs - Poles, Russians etc who died when the Germans invaded their countries. The German invasion of Russia ("Barbarossa") was probably the most brutal and hideous conflict of the war. The Russians were regarded as "untermensch" and the Germans felt that they had the right to slaughter them like animals, and they did. The killed for plunder, they killed to terrorise the population into submission, they killed as part of a scorched earth policy to prevent any Russian troops to be able to live off the land - millions of people who weren't directly murdered died of starvation because the German army stole everything, and what they couldn't carry away they destroyed.
However the total annihilation of other races wasn't intended - it was a means to an end (the end being the annihilation of the Jews and the domination of Europe by Aryans). In fact, Hitler had intended to make slaves of the Poles and Russians in the service of Germany.
"Holocaust" has now become a term pretty much synonymous with genocide, and there have been other holocausts since. There have probably been similar slaughters before in early history, but this one was different.
Hitler's Holocaust is unique in that it was the first time that an entire nation was turned into a factory killing machine dedicated to destroying, in its entirety, another race. It was the first time that camps and killing methods were developed with the sole purpose of mass murder of a people purely because of their race.
Even when stopping the killing, and diverting the manpower who staffed the camps to the frontline would have been in Germany's interests, the murder - the transportations, the gassings - continued to the bitter end.
The Jews were the only people that this hatred was extended to. Yes - others were killed in large numbers, and often brutally - but no nation was so singled out for destruction.
To employ the term "Holocaust" because some men regard being correctly identified as male, and claim that this is "literal violence", is sickening, and demeaning to all who suffered.
Edit for grammar