What is Mvar? reactive power in generation process and how can we calculate it?

In electric power transmission and distribution, volt-ampere reactive (var) is a unit by which reactive power is expressed in an AC electric power system. Reactive power exists in an AC circuit when the current and voltage are not in phase. The correct symbol is var and not Var, VAr, or VAR,[1] but all three terms are widely used, and VAR is widely used throughout the power industry infrastructure. The term var was proposed by the Romanian electrical engineer Constantin Budeanu and introduced in 1930 by the IEC inStockholm, which has adopted it as the unit for reactive power.