Definition of Overton window in US English:

Overton window

noun

the Overton window
US
  • The spectrum of ideas on public policy and social issues considered acceptable by the general public at a given time.

    ‘I suppose the Overton window is shifting, but slowly’

Origin

Early 21st century: named after Joseph P. Overton (1960–2003) former vice president of the Mackinac Center for Public Policy in the US, who developed the concept.