= Solution
<Universality classes> identify systems with the same long-distance <renormalization-group fixed point>. Spatial dimension, <order parameter> symmetry and number of components, and the range of interactions help determine the equilibrium class. Microscopic lattice details and many local interactions become <irrelevant operators> under coarse-graining. Universal quantities include <critical exponents>, scaling functions after fixing metric normalizations, and suitable amplitude ratios. The critical temperature, bare couplings, absolute correlation-length and susceptibility amplitudes, analytic <free-energy density> backgrounds, and microscopic length scales are generally not universal. Dynamic universality can additionally depend on conservation laws, so it should not be inferred solely from a static scalar potential.
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