The story
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A phenomenon indicating that a particular technology is or was used by a particular society; (astrophysics, astrobiology) a phenomenon indicating that a particular technology is or was present in some place (for example, a phenomenon suggesting that a Dyson sphere might exist in a certain region of space). Full definition →
Etymology from Wiktionary, CC BY-SA 4.0.