Plain English Meaning
Dirty, hazy air caused by pollution mixing with the atmosphere. It makes the air look murky and reduces how far you can see through it.
Full Definition
A form of air pollution consisting of a mixture of smoke, industrial emissions, vehicle exhaust, and atmospheric haze that reduces visibility and can persist near the surface, particularly in urban areas or under stable atmospheric conditions.
Context Anchor
Encountered in weather and night vision discussions, especially when checking whether visibility will be good enough for safe visual flying.