Depending on the pressure and temperature, the air can only retain a certain amount of humidity, when this limit is exceeded, the humidity condenses into water vapour.
This limit is identified in relative humidity equivalent to 100%. The lower the percentage value, the more relative humidity in the air is far from reaching the saturation point.
Relative Humidity
The relative humidity indicates the percentage of humidity in relation to that which the air is able to retain before it reaches the saturation point.