What is "exformation"

n. All the shared body of knowledge which is not explicitly used when people communicate, but without which communication would be impossible

Exformation (originally spelled eksformation in Danish) is a term coined by Danish science writer Tor Nørretranders in his book The User Illusion published in English 1998. It is meant to mean explicitly discarded information. However, the term also has other meanings related to information, for instance "useful and relevant information" or a specific kind of information explosion.