Humidity is water vapor which exists in the air, almost all air particles actually hold water, but in some cases they hold a great deal more than normal. This additional water in the air can be a result of heat arriving after a rain shower, water vapor as a result of people talking in a confined space such as car or owing to evaporation of water into a gas like state. There are a great many industries which must regulate the amount of water which is in the air in order for them to avoid issues,