What is a Superhero?

It''s easy to name a superhero--Superman, Batman, Thor, Spiderman, the Green Lantern, Buffy the Vampire Slayer, Rorschach, Wolverine--but it''s not so easy to define what a superhero is. Buffy has superpowers, but she doesn''t have a costume. Batman has a costume, but doesn''t have superpowers. What is the role of power and superpower? And what are supervillains and why do we need them? In What is...