What is known by perceptual experience and reasoning. For example, 1234567.89 is data; "Your bank balance has jumped 8087% to $1234567.89" is information; "Nobody owes me that much money" is knowledge; and "I'd better talk to the bank before I spend it because of what has happened to other people" is wisdom. [Free On-line Dictionary of Computing] Explicit knowledge is formal and codified, e.g., documents, databases, knowledge bases. Tacit knowledge is informal and uncodified, e.g., that found in the heads of employees, customers, vendors. It is experiential, ephemeral, transitory, and difficult to document [Carla O'Dell & C.Jackson Grayson]. It is internalized by the knower over a long period of time, and incorporates so much accrued and embedded learning that its rules may be impossible to separate from how an individual acts [Thomas Davenport & Laurence Prusak]. Compare with data and information.