Insider

An insider is a member of any group of people of limited number and generally restricted access. The term is used in the context of secret, privileged, hidden or otherwise esoteric information or knowledge: an insider is a "member of the gang" and as such knows things only people in the gang know.

In our complicated and information-rich world, the concept of insider knowledge is popular and pervasive, as a source of direct and useful guidance. In a given situation, an insider is contrasted with an outside expert: the expert can provide an in-depth theoretical analysis that should lead to a practical opinion, while an insider has firsthand, material knowledge. Insider information may be thought of as more accurate and valuable than expert opinion.