I think they're insiders if they know something's about to happen the general public isn't privy to that will affect the market. I don't think you need to be part of a company to be an insider. For instance, you could be part of a regulatory board knowing you were about to open up restrictions on something that would enable a company to make money in a sector it was previously outlawed from and it would be only natural to invest in that company before the regulatory change went public.