A person who derives sexual pleasure or gratification from a
bellybutton belly area. Use of bellybutton or belly area for gratification when other sources of gratification are unavailable doesn't count, there has to be a preference for the bellybutton(s) or the belly area.
There appears to be no differentiation between those who prefer 'innies' and those who prefer 'outies' but most bellyfetishists have a strong preference. Many bellyfetishists are also activists for getting certain items onto the Feature Request for Human 2.0.
see also: belly button, bellybutton, fetishist