Anschluss is a German word that means "joining together" in English. In history, it is used to talk about a time when Germany wanted to join together with Austria.
Imagine you are at a playground, and you really want to play with a group of kids who are already playing together. You try to join their game, but they say no because they don't want you to play with them.
This is what happened when Germany wanted to join Austria in 1938. Some people in Germany thought Austria should be a part of Germany because they were both German-speaking countries. But the people of Austria didn't want to join Germany.
However, the leader of Germany at the time, a man named Adolf Hitler, wanted Austria to be a part of Germany whether the Austrians liked it or not. So, he sent his army into Austria, took it over, and made Austria a part of Germany. This is what is called the Anschluss.
It was not a good thing because it showed how Germany was using force to take over other countries. This eventually led to the start of World War II.