green light

green colored light which signals that it is safe to proceed; go-ahead signal

Things commonly known as a Green Light include:A traffic lightA fishing light attractorA greenlight — formal approval of finance for film productionGreen Light (novel) — a 1935 novel by  Lloyd C. DouglasGreen Light (film) — a 1937 film starring  Errol Flynn"Green Light" (song) — a song from Beyoncé Knowles's album B'DayGreenLight — the  European Union program to reduce lighting energy use.
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To greenlight a project, in the context of the movie and TV businesses, is to formally approve production finance, thereby allowing the project to move forward from the development phase to pre-production and, barring disasters, principal photography. A project which is financed is said to be greenlit or greenlighted and a studio executive who has authority to grant greenlight status to a project is said to have greenlight power.
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Noun
1. a signal to proceed
(synonym) go-ahead
(hypernym) traffic light, traffic signal, stoplight
2. permission to proceed with a project or to take action; "the gave the green light for construction to begin"
(hypernym) permission