Plain English Meaning
The decision the pilot makes about whether it is safe to fly today. The answer is either yes, go, or no, do not go. There is no middle option.
Full Definition
The pilot's final determination, made before flight, of whether to proceed with the planned flight or cancel it, based on a complete assessment of the pilot, aircraft, environment, and external pressures. It is a binary choice: either all factors support a safe flight, or the flight does not begin.
Context Anchor
Used before departure and any time conditions change, especially when using the PAVE checklist to look at the pilot, aircraft, environment, and outside pressures.
Derivation
The phrase comes from simple command language: “go” means proceed, and “no-go” means do not proceed. In aviation, it helps because the decision must be clear enough to act on, not just a vague feeling that things seem okay or not okay.