ELI5: Explain Like I'm 5

Property is theft

Property is theft is an idea that everything that is owned by someone is usually taken from someone else. This means that people who own lots of money, land, and possessions probably got those things from someone else, such as stealing it or taking it away from them unfairly. People who don't have lots of money or possessions can feel like they're being wronged, because the rich people have stuff that was taken from them.