  In this paper we discuss the fluidity of the hot and dense QCD matter created
in ultrarelativistic heavy ion collisions in comparison with various other
fluids, and in particular suggest its possible supercriticality. After
examining the proper way to compare non-relativistic and relativistic fluids
from both thermodynamic and hydrodynamic perspectives, we propose a new
fluidity measure which shows certain universality for a remarkable diversity of
critical fluids. We then demonstrate that a fluid in its supercritical regime
has its fluidity considerably enhanced. This may suggest a possible
relationship between the seemingly good fluidity of the QCD matter produced in
heavy ion collisions at center of mass energy of $\sqrt{s}=200 \rm AGeV$ and
the supercriticality of this matter with respect to the Critical-End-Point on
the QCD phase diagram. Based on such observation, we predict an even better
fluidity of the matter to be created in heavy ion collisions at LHC energy and
the loss of good fluidity at certain lower beam energy. Finally based on our
criteria, we analyze the suitability of a hydrodynamic description for the
fireball evolution in heavy ion collisions at various energies.
