National health insurance means that everyone in a country has access to medical care when they need it, no matter how much money they make or where they live. For example, if you get sick and need to see a doctor, you can go to any medical center or hospital and get the help you need without worrying about how much it costs. It's like having a big piggy bank that everyone puts in money to, so that when someone gets sick, they can use it to pay for their medical care. This helps to make sure that everyone in the country can stay healthy, even if they don't have a lot of money.