A royal charter is like a special paper that the king or queen gives to a group of people to allow them to do special things that other people can't do. It's like a very special permission slip.
For example, if a group of people wants to start a school or a hospital, they might need lots of money and special rules and laws to make sure they do things the right way. So, they might ask the king or queen for a royal charter to start their school or hospital.
The royal charter will say what the group can and can't do, and it will also give them special privileges, like not having to pay certain taxes.
Once the group gets their royal charter, they become a special kind of organization that has certain responsibilities and privileges that other groups don't have.