This idiom means to grant permission or approval to proceed with a plan, project, or action, signaling that all obstacles have been cleared. It evokes the image of a green traffic light allowing movement, suggesting readiness and authorization. The phrase is used in business, creative, or bureaucratic contexts to indicate official sanction, carrying an encouraging or decisive tone. It reflects cultural associations of green with progress and the modern reliance on clear signals for action, often implying a moment of opportunity or forward momentum.

The phrase originated in early 20th-century America, tied to the introduction of traffic lights in the 1910s, where green signaled ‘go.’ An early metaphorical use appears in a 1928 *New York Times* article, describing a project ‘given the green light’ by authorities. The idiom gained traction during the 1930s, reflecting America’s growing infrastructure and bureaucratic systems, as seen in John Steinbeck’s *The Grapes of Wrath* (1939). Its use grew in the mid-20th century, particularly in corporate and governmental contexts, and spread to British English through American media and globalization. The phrase’s clear imagery and relevance to decision-making ensured its widespread use, especially in fast-paced industries.