A character (usually the protagonist) is extremely powerful. They could sneeze and destroy an army, they have a sword that can cut through literally anything, they have an unlimited supply of level one million magic.
Sometimes, it's played for laughs, but more often the character will pretend to be normal, maybe to escape unwanted attention, and only use their real power when they're in a pinch. Of course, the fact that they can just do this whenever they're in a pinch means that the audience knows they're never going to lose, so there's not much tension from the physical threats they encounter.
In a good story, the drama will be provided through relationships with other characters, or some other difficulty that isn't obviated by the character's strength. In a bad story, the author will just pretend like the attacking monsters are a real threat, and then have the character pull out a super-power and go "gosh, sure is a good thing I'm more powerful than god!", as though there were ever any doubt.