A comic book is a colourful magazine which presents a story in graphic format with dialogue indicated with work or thought balloons. The guys collect comic books religiously. Wednesday night is New Comic Book Night because it's the night the new comic books arrive at the local comic book store. Howard has a collection of Robin comics. Sheldon collects Batman comics. Leonard states that he owns 2600 Superman comics (0102).
The guys discuss, debate, and speculate about the story lines and the capabilities of various comic book characters. These discussions range from intricately detailed, such as the debate in Penny's apartment between Sheldon and Stuart about the evolution of the character of Robin after the death of Batman (0222), to the ridiculous, such as the discussion about how Superman might clean mustard off of his uniform after an evening meal in the Bottle City of Kandor (0212). They also have many collectable comic book-related items around their apartment, such as a Batman cookie jar and a large-scale action figures.