$\omega=\omega_{0} .$ This frequency is known as resonance frequency. Amplitude of oscillation for a forced, damped oscillator is
$A=\frac{F_{0} / m}{\sqrt{\left(\omega^{2}-\omega_{0}^{2}\right)+(b \omega / m)^{2}}}$
where $b$ is constant related to the strength
of the resistive force, $\omega_{0}=\sqrt{k / m}$ is natural frequency of undamped oscillator$(b=0)$.

