Vapor The Simple English Wiktionary has a definition for: vapor. Vapor (British English: vapour) is a mass of small drops of liquid which fly in the air, for example because the liquid has been heated. The temperature at which each material turns into vapor is determined according to the air pressure. This short article about science can be made longer. You can help Wikipedia by adding to it. Retrieved from "https://simple.wikipedia.org/w/index.php?title=Vapor&oldid=6907167"