What is Halo (ring) in Halo?

Question

Im not a total idiot, but i want to know what it is and what it does. my friend told me few stuff, but i didnt get it.

Answer 1

Ive only ever palyed MP with my mates and i know its a Super weapon left by "The Forerunners" who fired them off thousands of years ago to wipe out The Flood, they are layed around galaxy so can kill all life forms around the galaxy. ( The Flood die out if theres no life forms to feed off)

Earth is jsut on the edge of the blast radius and houses the Arc, which leads to the on button.

Answer 2

The Halo itself is a weapon. When fired, it's able to pretty much decimate anything around it (planets included) and exterminate all life.  It was in a system with a few other Halo's in that particular galaxy, all of which had an overlapping blast radius, thereby expanding the damage.

Answer 3

its a planet shaped like a ring