A sub-genre of superhero fiction which deconstructs the conventional idea of a superhero, demonstrating the kind of person who would want to beat up bad guys at night, and the mental and physical hardships that would come out of that. The hero doesn't have any powers (or otherwise they're nothing too spectacular), and just wanders the streets at night beating up thugs and mafia members in a vigilante quest for justice; usually because of some psychological problem they have. The genre was born out of the popularity of The Dark Knight Saga and the recent reserge in popularity for Watchmen; although neither works exactly fit the trope, they served as the inspiration for later works.
Hello, Unknown Troper. You'll need to get known to lend a hand here.