Communism is an idea that tries to make sure everyone has equal stuff. It started a long time ago, in the 1800s, when people thought it wasn't fair that some people had a lot of money and other people didn't have much at all.
Karl Marx, a smart man, came up with the idea of communism. He thought that everyone should work hard, and then everyone should have an equal share of the stuff they need to live, like food and clothes and houses.
Communism was popular in some countries, like Russia and China. The leaders in those countries said they were going to make sure everyone had equal stuff. But things didn't always work out that way. Sometimes people in charge of the country took too much power and didn't want to share with everyone else.
Some people still believe in communism today, because they think it's a good idea. But other people don't like it because they think it takes away people's freedom.