The medium is the message is a phrase coined by Marshall McLuhan meaning that the form of a medium embeds itself in the message, creating a symbiotic relationship by which the medium influences how the message is perceived. The phrase was introduced in his most widely known book, Understanding Media: The Extensions of Man, published in 1964.[1] McLuhan proposes that a medium itself, not the content it carries, should be the focus of study. He said that a medium affects the society in which it plays a role not only by the content delivered over the medium, but also by the characteristics of the medium itself.

“Hot” and “cool” media
In the first part of Understanding Media, McLuhan also 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.[42]
“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.” [43]