In McLuhan’s most popular book “Understanding Media: The Extensions of Man “, he claims that “the medium is the message” and explains that a medium affects the society in which it plays a role not by the content delivered over the medium, but by the characteristics of the medium itself.
He also proposes two frames for categorizing the media as “hot” and “cool” according to different sensory effects associated with the media.
Hot media are low in audience participation due to their high resolution or definition. Cool media are high in audience participation due to their low definition (the receiver must fill in the missing information).
In other words; hot media requires little information to be filled in by the receiver i.e. radio, film, lecture, print are full of information and allow less involvment or less sensory completion. However cool media such as seminar, telephone, television, which are relatively lacking in information and require a higher sensory involvement of the user and higher participation.
Marshall Mcluhan Full lecture: The medium is the message – 1977 in this video you can find McLuhans’ lecture about the subjects of media that i’ve mentioned above.