Universal features of the order-parameter fluctuations

The universal scaling laws of order parameter fluctuations in any system in which the second-order critical behavior can be identified are discussed. These scaling laws can be derived rigorously for equilibrium systems when combined with the finite-size scaling analysis. The relation between order parameter, criticality and scaling law of fluctuations has been established and the connexion between the scaling function and the critical exponents has been found. (author)