An insider in a public company is anyone as director or above. But also, spouses of CEO, CFO, etc. An insider may or may not own shares, but they DO know what is going on 'inside' the company, and are thus banned from buying or selling stock except within the 30 days after filing fins. Been there, done that.
Banks and other financial institutions may also be considered insiders, if they gain any information that is not available to the public.
In short, anyone that has non-public information about a company, and profits from that knowledge, is breaking the law.