It is always hard to nail down genres to "the one single thing". They are usually a whole collction of things, that assembled together in some form, makes the genre, but not one single thing defines it all, because that single thing might also exist in other genres. And, genres aren't tight boxes. They overlap a lot.
Most superhero stories kinda play in a contemporary setting and involve individuals with unusual abilities that fight against criminal or evil entities (groups, people, individuals) of all kinds of sorts, some of their adversaries also utilizing (or being) individuals with unusual abilities. These abilities are often beyond human capabilities, sometimes supernatural, alien or relying on speculative/fictional technologies. The superheroes might act entirely outside (or outside raditional) governmental/public oversight/the law, for examples as vigilantes, mercenaries, spies or private detectives. The individuals might have secret identies to protect friends and family or help them evade the law and their adversaries. They often have distinct looks, like costumes or styles that allow distinguishing them from others.