Say you've worked in a specific industry for a long time and you know all the players. You know where the technology is, what the challenges are and where the tech is going. You know how key companies are managed, you have an idea about their goals and strategies. You know who's best positioned for what's coming. This is just general knowledge that you've acquired through your job over the years. Now say you've made enough money and retire. Because you know a thing or two about your industry you decide to buy or sell some stock. Can this be called insider trading? Perhaps. Is it illegal? Most likely not. Can you derive alpha from it? Hell yea.