What is Not Invented Here?

Legal Definition
Not invented here (NIH) is a stance adopted by social, corporate, or institutional cultures that avoid using or buying already existing products, research, standards, or knowledge because of their external origins and costs.

The reasons for not wanting to use the work of others are varied, but some can include fear of patent infringement, lack of understanding of the foreign work, an unwillingness to acknowledge or value the work of others, jealousy, or forming part of a wider turf war. As a social phenomenon, this philosophy manifests as an unwillingness to adopt an idea or product because it originates from another culture, a form of tribalism.

The term is normally used in a pejorative sense. The opposite predisposition is sometimes called "proudly found elsewhere" (PFE) or "invented elsewhere".
-- Wikipedia
Legal Definition
A negative attitude that is used to shoot down constructive suggestions or improvements to a situation.