  Freeze-out of particles in relativistic hydrodynamics is considered across a
3-dimensional space-time hypersurface. The conservation laws for time-like
parts of the freeze-out hypersurface require different values of temperature,
baryonic chemical potential and flow velocity in the fluid and in the final
particle spectra. We analyze this freeze-out discontinuity and its connection
to the shock-wave phenomena in relativistic hydrodynamics.
