The Overton window is a concept in political theory, named after its originator, Joe Overton, former vice president of the Mackinac Center for Public Policy. It describes a “window” in the range of public reactions to ideas in public discourse, in a spectrum of all possible options on an issue.
Overton described a method for moving that window, thereby including previously excluded ideas, while excluding previously acceptable ideas. The technique relies on people promoting ideas even less acceptable than the previous “outer fringe” ideas. That makes those old fringe ideas look less extreme, and thereby acceptable. The idea is that priming the public with fringe ideas intended to be and remain unacceptable, will make the real target ideas seem more acceptable by comparison.