the.com/fire ring

means A ring of stones (or a metal container) that contains a campfire so it burns where you want it and nothing else.

from A plain compound of 'fire' and 'ring' — describing exactly what it is, a ring-shaped boundary for fire. No hidden story here: it's a functional, literal name, likely formalized as campgrounds and park services began requiring contained fire pits for safety rather than letting campers build fires wherever they pleased.