Plain English Meaning
The air is clear enough that nothing in the atmosphere is blocking how far the pilot can see.
Full Definition
A flight visibility condition in which there are no atmospheric obscurations such as haze, mist, smoke, fog, or precipitation reducing how far a pilot can see. In practice it means visibility is sufficient that distance is no longer the limiting factor for visual reference outside the aircraft.
Context Anchor
Seen in training scenarios, weather descriptions, and instructor discussions when visibility is not intended to be a challenge in the lesson.