Answer: Insider trading
Step-by-step explanation:
Insider Trading refers to when a person trades on material non-public information. It is frowned upon because it gives an unfair advantage to people who know the internal affairs of a company such that they benefit at the expense of others.
Material non-public information refers to information that the public does not know about but can be reasonably expected to impart stock prices if the public knew.
Jeff knows information that is both material and non-public and acted on it thereby profiting at the expense of those who bought his shares as their stake will reduce and they will make losses when the stock price goes down.