The weather phenomenon that is a visible aggregate of tiny droplets reducing visibility is known as ____.

The weather phenomenon that is described as a visible aggregate of tiny droplets that reduces visibility is called fog. Fog forms when the air temperature drops to the dew point, causing water vapor in the air to condense into tiny water droplets that hang in the atmosphere. This creates a thick, cloud-like layer close to the ground, significantly hindering visibility, often to less than 1 kilometer.

While clouds are also made up of tiny water droplets, they typically exist at higher altitudes and do not necessarily result in reduced visibility at ground level. Mist is similar to fog but is generally less dense, allowing for better visibility, typically more than 1 kilometer. Overcast refers to a sky that is completely covered by clouds, but it does not specifically denote the visibility issues caused by suspended droplets in the air. Therefore, the correct answer is indeed fog, as it specifically indicates the reduction in visibility due to high concentrations of condensed water droplets in the air.