What's the difference between an principal, owner, president, and CEO?

As a non public corporation (as I ume you haven't issued any stock) you hold the office of President. CEO is a title normally reserved for the highest ranking executive in a publicly traded corporation. Not all CEO's are owners however. The title owner and the title principal mean the same thing. Although a principal isn't always 100% owner but at a minimum is the majority owner. What this all boils down to, is that your most appropriate title is President. Good luck to you!!