Final answer:
Humidity is the measure of moisture in the air compared to the maximum possible amount of water vapor that the air can hold. It depends on temperature and influences the formation of fog. Hot air can hold more water vapor than cold air.
Step-by-step explanation:
Humidity, specifically relative humidity, is the measure of moisture in the air compared to the maximum possible amount of water vapor that the air can hold. At its maximum, which is called saturation, the relative humidity is 100%. The amount of water vapor the air can hold depends on its temperature. For example, as the air temperature declines in the evening, relative humidity rises and can sometimes reach the dew point, where it is 100%. This can result in fog formation when water droplets condense in the air. Blowing hot air over something is more effective for drying because hot air can hold more water vapor than cold air.