No interest: Self-explanatory.
Passing interest: You may be interested now, or had once been interested, but are now no longer interested or suspect that you won't have an interest in it in the near future.
Moderate interest: You spend a casual amount of time pursuing your interest. It's not important, but it's not insignificant, either. The future of your interest is uncertain, save that it won't be short-lived.
Significant interest: Whatever you're interested in consumes much of your time and available resources, perhaps to the point where you wouldn't know how to fill a void without it. You probably can't imagine the possibility of losing interest in it during the rest of your life.