What is meant by relative humidity?

the amount of moisture contained / maximum moisture that air can contain as per those parameters

The relative humidity  of an air-water mixture is defined as the ratio of the   partial pressure of water vapor  in the mixture to the equilibrium vapor pressure of water  at a given temperature

Relative humidity is normally expressed as a percentage; a higher percentage means that the air-water mixture is more humid.

percentage of humidity saturation, if say30%RH, it is30% saturated..