High Quality Content by WIKIPEDIA articles! A cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth`s atmosphere are studied in the cloud physics branch of meteorology. Two processes, possibly acting together, can lead to air`s becoming saturated: cooling the air or adding water vapor to the air. In general, precipitation will fall to the surface; an exception is virga, which evaporates before reaching the surface.