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.
The term is a reference to the green traffic signal, indicating "go ahead." "Redlight" as a companion term to "greenlight" has not yet arisen to comparable eminence.
Executives who have true greenlight power are few and far between. It is usually the case that only one person in any given financing entity has true greenlight power and that those who have nominal greenlight power in the management structure beneath them must seek his or her approval for projects which they wish to greenlight.
The term "greenlight" has managed to find its way into general business and military culture as a result of its use in the film industry.