The Medium is The Message
Marshall McLuhan

In the first part of Understanding Media, Marshall McLuhan stated that different media invite different degrees of participation on the part of a person who chooses to consume a medium. Some media, like the movies, were "hot" that is, they enhance one single sense, in this case vision, in such a manner that a person does not need to exert much effort in filling in the details of a movie image. McLuhan contrasted this with "cool" TV, which he claimed requires more effort on the part of the viewer to determine meaning, and comics, which due to their minimal presentation of visual detail require a high degree of effort to fill in details that the cartoonist may have intended to portray. A movie is thus said by McLuhan to be "hot", intensifying one single sense "high definition", demanding a viewer's attention, and a comic book to be "cool" and "low definition", requiring much more conscious participation by the reader to extract value.

"Any hot medium allows of less participation than a cool one, as a lecture makes for less participation than a seminar, and a book for less than a dialogue."

Hot media usually, but not always, provide complete involvement without considerable stimulus. For example, print occupies visual space, uses visual senses, but can immerse its reader. Hot media favour analytical precision, quantitative analysis and sequential ordering, as they are usually sequential, linear and logical. They emphasize one sense (for example, of sight or sound) over the others. For this reason, hot media also include radio, as well as film, the lecture and photography.

Cool media, on the other hand, are usually, but not always, those that provide little involvement with substantial stimulus. They require more active participation on the part of the user, including the perception of abstract patterning and simultaneous comprehension of all parts. Therefore, according to McLuhan cool media include television, as well as the seminar and cartoons. McLuhan describes the term "cool media" as emerging from jazz and popular music and, in this context, is used to mean "detached."

This concept appears to force media into binary categories. However, McLuhan's hot and cool exist on a continuum: they are more correctly measured on a scale than as dichotomous terms.

- Ref.: en.wikipedia.com