The concept of tacit knowing comes from scientist and philosopher Michael Polanyi. It is important to note that he wrote about a process (hence Tacit Knowing) and not a form of knowledge. However, his phrase has been taken up to name a form of knowledge that is apparently wholly or partly inexplicable...as opposed to formal, codified or explicit knowledge. http://en.wikipedia.org/wiki/Tacit_knowledge
cannot be codified, but can only be transmitted via training or gained through personal experience (Master And Apprentices)
Here's a case of lost knowledge needing to be re-created: maybe engineering archaeology will always exist. The more I look around, the more the engineering world, once you go back more than a few years, looks like subterranean New York City. A mass of strange engineering feats humming away out of sight, produced by long-forgotten ancient peoples, leaving only fragmentary maps and diagrams.