MM从电视术语中引用了“高级”和“低级定义”。高级定义，比如说一张地图，指的是明确的、视觉上详细的定义。低级定义指那些眼睛一扫而过所形成的不清晰图像，需要看的人去填补那些未看清的空缺部分，比如说素描。M说电视是一个冷的、低定义的媒体，它只提供很少的信息却需要使用者以全部的感官投入其中。而书籍，M解释道，是一种热的、高定义的媒介，向使用者呈现大量的信息却只需要他们较低程度的感官参与。
Marshall McLuhan adapted these references from the TV jargon "high" and "low definition." High definition means well-defined, sharp and detailed visually, such as a map. Low definition refers to indistinct images scanned by the eye, with which the viewer is left to fill in the blanks, such as a sketch. McLuhan says television is a cool or low definition medium, offering little information but the user participates with most of his senses. He explains that a book is a hot or high definition medium, presenting the user with lots of information at a level of lower sensory participation.
