Definition of fringe noun from the Oxford Advanced American Dictionary

fringe

noun
/frɪndʒ/
 
 
1 [countable] a strip of hanging threads attached to the edge of something to decorate it2 [countable] the outer edge of an area or a groupon the northern fringe of the citythe urban/rural fringethe fringes of societyNina remained on the fringe of the crowd.3 [singular] usually the fringe groups of people, events, and activities that are not part of the main group or activityStreet musicians have been gathering as part of the festival fringe.fringe meetings at the party conferenceIDIOM

the lunatic fringe

(disapproving) those members of a political or other group whose views are considered to be very extreme and crazyThey stressed that only the lunatic fringe of the movement was involved in the incident.the lunatic fringe