Imagine you go to a big school where many kids go. Your teacher always writes your name on your work so that she knows who did it. This is called the "real-name" system.
Now, let's say you also want to play a game with your friends, but you don't want anyone to know who you are. You could use a nickname or a pretend name.
But sometimes, using fake names can be bad because people might not act nicely if they don't have to show their real identity. That's why some websites or apps use the real-name system to make sure everyone is accountable for what they say or do online.
For example, when you make a Facebook account or play some online games, you usually need to provide your real name to make an account. This way, people are more likely to be kind and respectful to each other because they know they can be held responsible for their actions.