The phrase "outer fringes" refers to the very edges or boundaries of something, typically an idea, a group, or a concept. It often describes the least mainstream or most extreme aspects of a particular subject. Full definition
The hydrogen and oxygen coronas of Mars are the tenuous outer fringe of the planet's upper atmosphere, where the edge of the atmosphere meets space. (sciencedaily.com)
The cells» dendrites form the feathery outer fringe, and the axons gathered in the middle dive into the depths of the cerebellum to send signals within. (discovermagazine.com)
That Greenland gets over 1m of snow fall each year (w.e.) means it is growing upwards at the same time as it's outer fringes of ice are melting back a bit. (climate-debate.com)