Permission or approval to proceed with a plan or project. It signals that obstacles have been removed and action can begin.
The phrase comes from traffic signals, where green lights indicate it's safe to proceed. This color-coded system was standardized in the early 20th century, and the metaphorical use followed as traffic lights became universally understood symbols.
The green light metaphor is so powerful because it taps into our learned response to traffic signals - we automatically associate green with 'go' and safety to proceed. This makes the phrase instantly comprehensible across cultures that use similar traffic systems, creating a nearly universal business and project management metaphor.
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