  An effective temperature $T_{\rm eff}$ which differs from the bath
temperature is believed to play an essential role in the theory of
elasto-plasticity of amorphous solids. The definition of a measurable $T_{\rm
eff}$ in the literature on sheared solids suffers however from being connected
to a fluctuation-dissipation theorem which is correct only in equilibrium. Here
we introduce a natural definition of $T_{\rm eff}$ based on measurable
structural features without recourse to any questionable assumption. The value
of $T_{\rm eff}$ is connected, using theory and scaling concepts, to the flow
stress and the mean energy that characterize the elasto-plastic flow.
