(Originally) the disc of the galaxy, as represented in the sky by the Milky Way; (later also) the relatively thin, disc-shaped outer part of any spiral galaxy.
Origin
Mid 19th century; earliest use found in The Eclectic Magazine.
Definition of galactic disc in US English:
galactic disc
(USgalactic disk)
noun
(Originally) the disc of the galaxy, as represented in the sky by the Milky Way; (later also) the relatively thin, disc-shaped outer part of any spiral galaxy.
Origin
Mid 19th century; earliest use found in The Eclectic Magazine.