What defines a hero? The dictionary defines it as "A person who is admired for courage or noble qualities". What defines a superhero? Powers? Weapons? Skills? All of these are components to a superhero yes, but to me what truly separates a hero from a superhero is one simple difference. A costume. Let me explain.
When a policeman or a firefighter put on their uniforms it readily identifies them. For a superhero their costumes ARE their uniforms and you could call them either and be correct. A costume for a superhero makes them a symbol.
To further elaborate I'll be using a character that has been the subject of many an argument over the years, Zorro
Zorro was created in 1919, years before Superman would appear and coin the term superhero. However Zorro shares many similarities to the traditional idea of a superhero. He fights crime and injustice, he helps people, he has a secret identity, he wears a mask and an easily identifiable costume, he has a secret hideout, he's extremely skilled in combat. Compare those qualities to a modern superhero and Zorro truly does fit the criteria to be a superhero.
However there are people that insist Zorro isn't a superhero. Their main argument is that since Zorro was created BEFORE the idea of a superhero he's simply a vigilante character that happens to share many similarities with traditional superheroes.
For a more modern example of what could fall under superhero guidelines is Casey Jones
Casey Jones is what most would indeed call a vigilante, but let's look at it like this. Casey actually does have a secret identity , his real name is Arnold Bernid Jones, with Casey being a nickname. He wears an easily identifiable outfit, hockey mask with a golf-bag full of sports equipment, and fights crime. Is he a hero or a superhero?
So what is the difference between a hero and a superhero? A hero is someone you may know, someone that proves themselves everyday without a costume. A superhero is someone that makes themselves more than just a man or woman and by putting on a costume they transcend mortality and become something timeless, something legendary.