  Strangeness enhancement is discussed as a feature specific to relativistic
nuclear collisions which create a fireball of strongly interacting matter at
high energy density. At very high energy this is suggested to be partonic
matter, but at lower energy it should consist of yet unknown hadronic degrees
of freedom. The freeze-out of this high density state to a hadron gas can tell
us about properties of fireball matter. The hadron gas at the instant of its
formation captures conditions directly at the QCD phase boundary at top SPS and
RHIC energy, chiefly the critical temperature and energy density.
