A Dyson Sphere is a hypothetical megastructure composed of a
massive sphere that surrounds a star, collecting as much of it's
energy as possible. Dyson spheres are named for Freeman Dyson,
who first proposed these structures. Dyson Spheres in Science
Fiction - In the Star Trek Universe, a Dyson Sphere made by an
unknown alien civilization was seen in TNG "Relics". - In the
Warhammer 40,000 universe, an ancient Dyson Sphere exists that
the Tyranid hive fleet Leviathan has avoided. This is believed
to be a C'tan construct. - In Mass Effect, the Geth are building
a Dyson Sphere.