Plain English Meaning
A day when the air looks milky or smoky, making it hard to see the horizon clearly even though you can still fly visually.
Full Definition
A day on which suspended particles in the lower atmosphere — typically dust, smoke, or fine moisture — reduce horizontal visibility and obscure the natural horizon, even though flight may still be legal under visual flight rules.
Context Anchor
Seen during visual flying, especially when using the horizon or ground objects to judge the airplane’s position and movement.
Derivation
‘Haze’ comes from an old English nautical term meaning thick or foggy air. A hazy day is one where the air carries enough fine particles to soften and blur what the pilot sees outside.