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Water vapor can take many forms.
Water vapor hangs in the air and takes different forms. It can become frost, dew, fog or clouds. What is fog?Fog is a collection of tiny water droplets that float in the air or near the earth's surface. Fog is the water which evaporates from bodies of water such as oceans,bays, lakes and rivers. Moisture evaporating from plants and soil adds to fog. This moisture hangs in the air.Fog is basically a cloud that touches the ground. Fog and clouds are made up of the same material, water vapor. Fog forms when moist air cools. When the air cools and there is more water vapor in the air than the air can hold, the water vapor begins to change into small droplets of water (condense). Fog disappears as the air temperature rises. This explains why fog is often seen in early morning and "burns off" (evaporates) as the sun climbs higher in the sky, warming the air temperature. 
What is Frost?Frost is water vapor which freezes. Frost occurs mainly on cold, cloudless nights when the air temperature drops below the freezing point (32°F or 0 °C). Frost forms on objects near the ground.Frost is sometimes called “hoarfrost”. Frost in gardening and farming Gardeners and farmers take note of the hard frost (25°F or-4°C) and killing frost of (32°F or 0°C) for their area. For most crops, planting can begin after all danger of frost has past. Spring and Fall both have two frosts, a killing frost and a hard frost. Both freeze the water in plant stems and kill or severely damage the plant. So, it is important to transplant most plants after the last frost occurs in the spring. In my region the last spring frost occurs around mid-April. The first fall frost occurs near mid-October. Once the frost hits in the autumn, plants are killed and the growing season is over. Local extension agencies and gardening clubs can provide information about frost dates in your area.
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