The avengers are commonly known as the superheroes that go together in the battlefield to save the city where their enemies are making them fight.
They fight together because of their same goal; to fight the bad guys and to live the people in the city in peace. This usually from different kinds of superheroes with different skills and special abilities with unique costumes to hide their true identities for their own good, other superheroes shows their faces but in normal lives, they’re still hard to be identify because of the way they act unlike the hero one. Well others really shows and people know it well.
Mostly, avengers can only be called avengers because they’re revenging from their enemies when they did something to its love ones, just like Spiderman; he is an avenger because of his uncle killed by the bad guy who happened to be his new enemy. While other avengers are becoming an avenger because they had given some extra ordinary abilities that no can had it.