Relative humidity is the term that specifically describes the ratio of the amount of water vapor present in the air to the maximum amount of water vapor the air can hold at a given temperature and pressure. This ratio is expressed as a percentage. For example, if the air holds half the maximum amount of moisture it could at that temperature, the relative humidity would be 50%.
Understanding relative humidity is important for various reasons, including weather forecasting and aviation, as it directly affects atmospheric conditions, visibility, and aircraft performance. This concept helps in predicting how much moisture can be expected in the atmosphere, which is integral to understanding weather patterns and phenomena like fog or precipitation. This distinguishes it from absolute humidity, which measures the total mass of water vapor per unit volume of air, independent of temperature and pressure. The saturation point refers to the maximum capacity of moisture that air can hold, while the dew point is the temperature at which air becomes saturated with moisture and water begins to condense.