Watchdog journalism is like a superhero whose job is to keep an eye on the bad guys and make sure they don't do anything bad.
When newspapers, TV stations, or websites do watchdog journalism, they investigate and report on things that the bad guys might be doing wrong: like stealing money, lying, cheating or breaking the law.
This kind of journalism is important because we need to be able to trust the people in charge, like the government or big companies.
If we can't trust them, then bad things might happen, like people getting hurt or losing their money. But by having watchdog journalists, we can keep watch on those in power and make sure they are doing the right thing.