Tribal knowledge

 ..... is any unwritten information that is known within a tribe but often unknown outside of it. A tribe may be a group or subgroup of people that share a common knowledge.
Tribal Knowledge is a term most often associated with a process step of the Six Sigma process. It is often referred to as knowledge 'known' yet undocumented such as information that has been handed down generation to generation with no documentation. Knowledge contained within a group that is assumed to be factual but has no known data or analysis to verify that it is factual. The Six Sigma community has adopted the term to use the description of 'tribe' as an analogy of a company. This term is sometimes considered derogative since in theory it has not been measured, thus proven. Source = Michael Nowlin
Tribal knowledge is any unwritten information that is not commonly known by others within a company. This term is used most when referencing information that may need to be known by others in order to produce quality product or service. The information may be key to quality performance but it may also be totally incorrect. Unlike similar forms of artisan intelligence, tribal knowledge can be converted into company property. It is often a good source of test factors during improvement efforts. Source = iSixSigma.com (definitions)

Continue reading at Wikipedia....