The Twilight Zone was a fantasy science fiction horror television series that aired on CBS in the 1960s.
Marty McFly made a reference to the show when he stated to Emmett Brown in 1955 that he "must be in the Twilight Zone". Doc found Marty's usage of the phrase as peculiar, and added "in a zone of twilight, neither here nor there, a middle ground, between light and shadow, between things and ideas...". Marty replied "Yeah I know, there's a signpost up ahead, you've just crossed over--"
Marty later used the Twilight Zone as a reference to scare George while as "Darth Vader".