I call a hero those who help others and keep their moral standards despite all the obstacles and deterioration which occur all around. Being a hero is not about being extremely brave or doing unusual things, saving humans lives or the whole world; if such things happen they deserve to be noticed and honoured, of course. However, I strongly believe that taking care of an ill person, or being honest while the surrounding people persuade to cheat are symptoms of heroism.
I'm sure that doing right things even, or maybe especially, when the doer is sure not to be noticed is what makes a real hero.