The Concept Humidity is a complicated concept.
Humidity refers to evaporated water substance in the air, i.e. water vapor.
For years relative humidity has been what we use to inform the TV audience, but it has many pit falls and to tell you the truth almost no one understands it, including many meteorologists. When thinking of humidity you always have to think in terms of energy. Of course this is expressed as temperature. There is only so much energy to go around and only a certain part of the thermal energy can go to do the work of evaporation. The rest goes to the other molecules in the air.