Correlation volume
= Correlation volume
{title2=$V_\xi\sim\xi^D$}
A <volume> over which order-parameter fluctuations are correlated. For one isotropic <correlation length> $\xi$, its scale is $\xi^D$; with anisotropic <lengths> it is the product of the appropriate directional <lengths>. A <Ginzburg criterion> compares fluctuations averaged over this <volume> with the squared mean <order parameter>.