Final answer:
Fog is the term used to describe a cloud layer at ground level that diminishes visibility to less than 0.6 mile or 1 kilometer, causing reduced visibility.
Step-by-step explanation:
The term for a cloud layer at ground level that reduces visibility to less than 0.6 mile (1 kilometer) is fog. Fog is formed when numerous tiny water droplets become suspended in the air, similar to clouds. However, unlike clouds that form high above the ground, fog forms at ground level and often results in poor visibility, which can affect various activities such as driving and aviation.
The term for a cloud layer at ground level that reduces visibility to less than 0.6 mile (1 kilometer) is fog. Fog is formed when air near the ground cools down and becomes saturated, causing water vapor to condense into tiny water droplets. These water droplets then suspend in the air, creating a thick cloud-like layer close to the surface.