All holders of financial community are entitled to parity of information. The question is whether a person had inside information, not whether the person is an insider. The majority rule in Common law was that the director or officer of a corp could trade in its stock without disclosing material nonpublic information concerning the corp that he acquired through his position. This is the concept of insider trading.
Under SEC section 10b(5), insider trading is not allowed. The general rule of thumb is the reasonable man/investor test. If a reasonable man knew the information, would he buy sell or hold with the information? Look at the probability of the event known by the insider and the magnitude of the profits if it came to be. The higher the probability and magnitude, the better chance it qualifies as insider information.
There is a window where the insiders may not trade. This window opens when hope of the event turns into expectancy. It closes again when there is full disclosure of all facts in the widest dissemination vehicle possible (usually, this is the Wall Street Journal).
This is not to say that officers who come into possession of material information are obligated to disclose the information if there's a valid business reason for nondisclosure. Rather it merely means that they may not profit from that information through transactions in the corporation's secutiries as a result of that nondisclosure. More later.