In Hebrew, Holocaust Remembrance Day is called Yom Hashoah.
Holocaust Remembrance Day is a day that has been set aside for remembering the victims of the Holocaust and for reminding Americans of what can happen to civilized people when bigotry, hatred and indifference reign. The United States Holocaust Memorial Council, created by act of Congress in 1980, was mandated to lead the nation in civic commemorations and to encourage appropriate Remembrance observances throughout the country.
Learn more here.
"First they came for the Communists, but I was not a Communist so I did not speak out. Then they came for the Socialists and the Trade Unionists, but I was neither, so I did not speak out. Then they came for the Jews, but I was not a Jew so I did not speak out. And when they came for me, there was no one left to speak out for me." — Martin Niemoeller
An interesting article, "The Holocaust’s Lessons for the Church" can be read here.
Other groups were also persecuted and killed by the Nazi regime, including some 220,000 Sinti and Roma (see Porajmos), as well as the disabled, homosexuals, Communists and other political prisoners, Jehovah's Witnesses, Polish citizens, and Soviet POWs (Ukrainians, Russians and Byelorussians). Many scholars do not include these groups in the scope of the Holocaust, defining it as the genocide of European Jewry, or what the Nazis called the "Final Solution of the Jewish Question" ("Die Endlösung der Judenfrage"). Taking into account all of the victims of Nazi persecution, the death toll rises considerably: estimates generally place the total number of victims at 9 to 11 million. (from Wikipedia)
What can you do today? Respond to the threats of Genocide and speak out. Look here.