tribal knowledge

A set of unwritten rules or information known by a group of individuals within an organization but not common to others that often contributes significantly to overall quality. Tribal knowledge may be essential to the production of a product or performance of a service but may also be counterintuitive to the process. For example, three chefs may create the same dish but each may have a level of unique variability. If a restaurateur wants to recreate a particular version of that dish on a continuing basis, they will have to retain the services of the chef that created it in that particular way.