RELATIVE humidity:It is defined as the ratio of the mass of water VAPOUR (mv) in a certain VOLUME of moist air to the mass of water vapour (MVS) in the same volume of saturated air (air having the maximum amount of water vapour without condensing) at the same temperature.It is denoted by ϕ.\(RH\;\left( \phi \right) = \frac{{{m_v}}}{{{m_{VS}}}}\)