astrophysics - What defines a cold plasma?

Been looking for this very simple answer for a while now, and google returns a face cream with the words cold plasma in it. Very frustrated.

Just wondering, what constitutes a cold plasma in the sense of the energies of the electrons and the energy of photons. Are we looking at non-relativistic photons and the electron velocities being quite slow? i.e.,

$$\beta<<\frac{h\nu}{mc^2}<<1$$

Or are we looking at mildly fast electrons,

$$\frac{h\nu}{mc^2}<<\beta<<1$$