The Wien's displacement law expresses relation between : -

Wien's displacement law: $\lambda_m T = b$, where $b = 2.9 \times 10^{-3}$ m K.
Here $\lambda_m$ is the wavelength at which the energy emitted by a black body is maximum, and T is the absolute temperature.
So the law relates the wavelength corresponding to maximum energy with the temperature: as T increases, $\lambda_m$ decreases.
So Wien's law expresses the relation between the wavelength corresponding to maximum energy and temperature.