What is Know-how?

Legal Definition
Know-how is a term for practical knowledge on how to accomplish something, as opposed to "know-what" (facts), "know-why" (science), or "know-who" (communication). Know-how is often tacit knowledge, which means that it is difficult to transfer to another person by means of writing it down or verbalising it. The opposite of tacit knowledge is explicit knowledge.

In the context of industrial property (now generally viewed as intellectual property - IP), know-how is a component in the transfer of technology in national and international environments, co-existing with or separate from other IP rights such as patents, trademarks and copyright and is an economic asset. While know-how is recognized in United States Tax regulations as a property, services by individuals having know-how are not.
-- Wikipedia
Legal Definition
The ability to achieve a practical end due to knowledge and/or skill. Know-how is intangible property, the rights to which a person may buy or sell.
Illustrative caselaw
See, e.g. Copperweld Corp. v. Independence Tube Corp., 467 U.S. 752, 757 (1984).
See also