Yes, a hero is a kind of sandwich. But when David Bowie sings, “We can be heroes,” he’s not talking about sandwiches. He’s talking about the more popular kind of hero — the kind who saves your life!
A hero is someone who does fantastic things that people love. The guy who rescues a skater from a frozen pond is a hero. A hero can be the main character of a story, too, if people root for him. Spiderman is the hero of the comic series: he's the central character, but he also saves people. The word hero goes back to the Greek, referring to a demigod.