Fog is a weather phenomenon that occurs when tiny water droplets are suspended in the air near the ground. This happens when the air cools and reaches its dew point, causing moisture to condense. Fog can reduce visibility significantly, making it difficult to see objects or navigate roads. There are different types of fog, including radiation fog, which forms on clear nights when the ground cools, and advection fog, which occurs when warm, moist air moves over cooler surfaces. Fog is common in coastal areas and valleys, and it can create a mysterious atmosphere in nature.