Legality refers to whether something is allowed or not allowed by the law. The law is a set of rules that everyone in a certain area or country must follow. If you break the law, you might get in trouble and have to face consequences like paying a fine or going to jail.
For example, it is legal to drive a car if you have a driver's license and follow the traffic rules. However, it is illegal to steal things or hurt someone on purpose.
The law can be very complicated, and there are different rules for different situations. Sometimes, even grown-ups have a hard time understanding it all. But it's important to know what's legal and what's not so that you can stay out of trouble and live a happy, healthy life within the bounds of the law.