Mainly, the Jews. Other groups targeted were the Gypsies, gays, and anyone who would oppose the Nazi government. Each group had their own triangle color, and sometimes they carried a strip.
The Nazis were interested in exterminating groups that they felt were inferior. Jews, disabled people, Slavic people, and gypsies were the groups that were exterminated on racial grounds.
Gypsies
Pure Aryans loyal to the Nazi party.
The only groups singled out for extermination rather than enslavement were the Jews and the Romanies ('gypsies'). Please see related question.
They were taken to extermination camps. Please see related question.
The term is the Holocaust.
The Nazis employed several different methods of extermination during the Holocaust. Most notably were gas chambers, firing squads, mobile extermination trucks, and labor camps.
Russians, Slavs, Poles, Jews, Gypsies, the weak and the lame, the mentally challenged, Homosexuals, Blacks, and others.....
Poland.
The word is the Holocaust.
After the 1st year of WWII.
The Holocaust, the attempted extermination of the Jews and other groups deemed "undesirable" by the Nazis, was based on the idea that the Germans were the "master race." In every respect, it was a violent expression of discrimination.