Comic Books: A medium. Everything from Spider-Man to Peanuts to Jimmy Corrigan to Battle Royale. Even “Comic Books” is probably overly precise, but it’s catchier than “Sequential Graphic Art.”
Superheroes: A genre. Well, kind of. Probably a sub-cross-genre of action/sci-fi/fantasy/adventure. But we’re calling it a genre for now. Generally speaking, people with extraordinary powers and/or abilities fighting similarly enhanced villains. Often, though not necessarily, with costumes. You can obviously nitpick all you want – in fact, Marvel and DC technically co-own the trademark to “superhero” – but practically speaking it can be anything from The Shadow and Superman to Heroes and Madman.
Superhero Comics: A genre within the medium. Hellboy and Amazing Spider-Man are both superhero comics. So are Nextwave and Sailor Moon and Swamp Thing and Seaguy.
Marvel & DC Superhero Comics: Superhero comics owned and published by two specific companies and aimed at a specific audience. Their marketing policy, at least as far as their superhero books are concerned, can be summed up allegorically by the president of the Southern Cracker Factory:
Crackers are a family food. Happy families. Maybe single people eat crackers, we don’t know. Frankly, we don’t want to know.