Answer:
the extermination of European Jews and others by the Nazis
Step-by-step explanation:
There have been lots of Holocausts in history, it just has a different meaning now compared to a hundred years before. The way we think of the word now is associated with what Adolf Hitler did in WWII. He decided that his idea of a good society was removing people he thought didn't matter the best way he knew how when he started to take over Europe. Sadly, that meant killing them and taking away all their belongings and trying to erase them from history. Hitler tried really hard and got rid of a lot of people living in Europe before he was stopped.
One group in particular, the Jews, adopted the term to have a religious meaning to what happened to them in Europe when Hitler took over. In their language (called Hebrew), the word means "an offering" to God, and felt what had happened to them and their families was a very sad, painful, sacrifice. So when we talk about Holocaust today, we mean the sad sacrifice made by this group, and others like them, because of what one bad person believed.