insider(n = noun.person) - an officer of a corporation or others who have access to private information about the corporation's operations;
is a kind of business executive, corporate executive

   an officer of a corporation or others who have access to private information about the corporation's operations, especially information relating to profitability.
"An insider is forbidden by U. S. securities laws to trade stock in publicly owned corporations based on the private information. The definition of insider for the purpose of securities law has changed in the late 29th century to become more inclusive, whereas it initially was applied only to officers of a corporation." [WordNet 1.5]

insider, n.
1 a person who is within a society, organization, etc. (cf. OUTSIDER).
2 a person privy to a secret, esp. when using it to gain advantage.

Idiom:
insider dealing Stock Exch. the illegal practice of trading to one's own advantage through having access to confidential information.

insider information, insider trading