It is defined as the ratio of the amount of heat removed in a cycle from the refrigerator to the work done by some external agency to help the removal of this heat, i.e.,
β = \(\frac{Q_2}{W}\) = \(\frac{Q_2}{Q_1-Q_2}\)
Also β = \(\frac{T_2}{T_1-T_2}\)
For higher efficiency of refrigerator, β should be higher.