Insider trading involves trading stocks or securities based on non-public information. It is considered illegal and unfair to other investors without access to that information. There are two types of insiders - primary insiders like directors, auditors, and top executives who have direct access to non-public company information, and secondary insiders like dealers and other employees who may have access to insider information. Examples of insider information include financial results, dividend declarations, mergers and acquisitions. Insider trading is prohibited, and those engaging in it may face penalties including fines up to 5 lakhs, criminal prosecution, and prohibited future dealings.