| Term | Definition |
| Water Vapor | An invisible gas formed when water reaches 100 degrees Celsius and evaporates. |
| Condensation | The change from water vapor to liquid water |
| Specific Humidity | The amount of water vapor in the air at a given time and place; expressed as the number of grams of water vapor per kilogram of air |
| Saturated | The condition in which the air is holding as much water vapor as possible at a given temperature and pressure |
| Relative Humidity | A comparison of the actual amount of water vapor in the air with the maximum amount of water vapor that can be present in the air at a given temperature and pressure |
| Dew Point | The temperature at which saturation occurs and condensation begins |
| Condensation Nuclei | Microscopic particles on which water vapor condenses to form cloud droplets |
| Psychrometer | An instrument used to measure humidity |