Media used to be simple. If you wanted the news, you bought a newspaper. You didn't have a lot of choices: maybe two or three to pick from. And these newspapers paid journalists to go out and find the news. If they wrote lies, those people would lose their jobs.
The Internet changed all that. Now there are thousands of news websites to choose from, and a lot of them are free. This means they cannot pay journalists. So how do they get their news? Maybe they get the information secondhand, from newspapers or other websites. Or maybe they just make it all up.
"Fake news" is news with inaccurate information. Sometimes this is on purpose. Sometimes it is because of a simple mistake. But fake news is a huge problem. It can even be hard to know what is real and what is not sometimes.
How can a reader spot fake news? Always think of the reputation of the website. Media companies and journalists care about their reputations. They might not be right all the time, but they won't try to trick their readers on purpose.