Marshall McLuhan (1911-1980), was a Canadian philosopher who concentrated his studies on media theory. He created this ‘Hot and Cool Media’ concept in the 1960’s.
Hot media is usually defined as being visual, using a single sense, such as printed or photographic documents. It is structured and complete, leaving little human input needed. Other examples of hot media include cinema, radio, books, and posters.
On the contrary, cool media requires several senses as it is low-resolution and therefore needs more energy from the receiver to determine meaning and sense of the content. Examples of this are the telephone, television, conversation etc.
I believe that McLuhan’s theory may have changed somewhat over the last fifty years in his classification of media. Technology has moved on drastically and continues to evolve rapidly conjoining elements from different means of communication. For example; smart phones, ipads and ipods etc. have built in cameras, touch screens (adding physical interaction) and the ability to access the internet. They are also able to send SMS and picture messages which would be considered as hot media, changing the telephone to be classed from cool to hot media.