Relative humidity indicates the amount of _____?

Relative humidity measures the amount of moisture in the air compared to the maximum amount of moisture that the air can hold at a given temperature. It is expressed as a percentage, indicating how close the air is to being saturated with water vapor. For example, a relative humidity of 50% means the air is holding half of the moisture it is capable of holding at that temperature. This concept is fundamental in HVAC and environmental control, as it affects comfort levels, mold growth, and the efficiency of heating and cooling systems. The other options relate to different aspects of air properties—heat refers to thermal energy, pressure refers to the force exerted by air molecules, and speed of air movement pertains to air circulation, all of which are separate from the measurement of humidity.