Damping factor - loudspeakers and headphones
'Damping factor' is defined as the ration of speaker impedance to output impedance. So, higher speaker impedance, more damping.

It's a fairly meaningless concept and indeed a pretty meaningless number by itself, especially as it is invariably referred to 8 ohms instead of an actual speaker impedance. The real item of interest is the amplifier's output impedance, and its variance with frequency. The lower the internal output impedance, the more effect negative feedback can have on unwanted currents appearing across the load impedance due to speaker non-linearity, flyback, reverse EMF etc.