medium is the message theory as practiced

Medium is the massage a phase coined by Marshall McLuhan, it means that the form of medium embeds itself in any message creating a symbiotic relationship by which the medium influences how the message is perceived.

the book; understanding media; the extensions of man by Marshall McLuhan explains this in more detail. 

for example a message can be printed r placed on something that will make you perceive it in a different way.   

This is an example of medium is the message. its a solar powered billboard advertisement in California its saying "this isn't a billboard" when in a matter of fact it is because its advertising solar power and then it proceeds to say "its a power plant" which technically it is because its producing its own power for its own light. It makes us question what it really is because of the message that is printed onto the billboard.