‘绿灯’ literally means 'green light'—the green signal in traffic lights that indicates it is safe to proceed. The character 绿 (lǜ) means 'green', and 灯 (dēng) means 'light' or 'lamp'. Together, they form a compound noun rooted in traffic terminology.

Figuratively, 绿灯 is widely used as an idiom meaning 'go-ahead' or 'official approval'—especially when authorities, institutions, or supervisors permit or facilitate something. You’ll hear it in business, government, education, and everyday conversation: e.g., 'give the green light to a project' becomes '为项目开绿灯'. It carries a positive, enabling connotation and is more formal than casual slang but still common in spoken and written Mandarin.