Hey kiddo, do you watch TV or read newspapers? These are called "mainstream media". They have news reporters who tell us what is happening in our country and around the world.
Mainstream media can be different types of media like TV news channels, newspapers, magazines or even websites. People working in mainstream media, like journalists, try to find out what is true and what is not. They write news reports that are meant to inform people about events happening around them.
Sometimes people think that mainstream media only reports bad news, but that's not true. They report all kinds of news, good or bad, happy or sad, so that people can stay informed.
It's important to know what's happening around us, and that is why newspapers, TV channels, and websites play an important role in our lives.