Question

what is the definition of absolute humidity?

Answer 1

ABSOLUTE HUMIDITY :-  density of moisture of water vapors in per unit                                                volume of air known as ABSOLUTE HUMIDITY. 

                                      - it is defined as kilogram per cubic meter. (kg/m3).

Answer 2

Absolute Humidity is the actual amount of water vapour in a given volume of air at a given temperature. 
It is measured in grams per cubic metre ( g/m³ or  $g m^{-3}$ ).