Gold standard for mulitcritical point

[physikerwelt]

I think the gold standard definition for T_c needs to be improved

As an example consider a substance ferromagnetic below a transition temperature T_{c} , and paramagnetic above T_{c} . The parameter space here is the temperature axis, and the critical manifold consists of the point T_{c} . Now add hydrostatic pressure P to the parameter space. Under hydrostatic pressure the substance normally still becomes ferromagnetic below a temperature T_{c}(P).