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 the corporate environment, when it comes to the publicly traded companies, an insider specifically refers to an executive who is privy to internal strategic direction and initiatives of the company. Insider’s transactions in the company stock are highly regulated as they could potentially be taking advantage of non-public information.