insider

Definition from Nolo’s Plain-English Law Dictionary

Someone who has a position in a business or stock brokerage, which allows him or her privy to confidential information (such as future changes in management, upcoming profit and loss reports, secret sales figures, and merger negotiations) which will affect the value of stocks or bonds. Use of such confidential information unavailable to the investing public in order to profit through sale or purchase of stocks or bonds is unethical and a crime under the Securities and Exchange Act.

Definition provided by Nolo’s Plain-English Law Dictionary.