Jerry...fair question. These are the definitions by which I define the two and can not be positively vetted by any dictionary or business terminology that I am aware of:
principal: An officer (President/CEO, VP, Secretary, Treasurer) and/or board member of the company in discussion. In Expo's case James D. Brown, Glenn Harrs, Jerry Elledge, Jimmy Kendrick and a mystery BOD member (or two) possibly to be named.
insiders: Often accredited investor(s), PIPE funders (or family/friends of the principals) who have insider contacts and may be on the "in" with company principals. In many pink sheet scams these investors are often given the "nod and a wink" when a P&D PR flurry is about to be released in order to pace the dump of their often large holdings of shares into it. I could name the usual suspects and PIPE funders surrounding Expo Holdings but since I have no proof of their status as to possession of shares at this time, the information would be irrelevant. Cash provided to the principals might be distributed as salaries, perks or bonuses through regular G&A channels, cash to the "insiders" through profitting from capital gains in EXPH shares. It would be almost impossible to prove any illegality in either case unless one of culprits dropped the dime on the others. Which is why all you really need in a case like Expo is to get one key person in a position where they could be facing time or life altering fines...then the whole house of cards usually comes tumbling down. All IMHO.