For the Q factor of a body undergoing force oscillations, does resonant frequency refers to the frequency of driving frequency or the body's natural frequency?

The term resonant frequency seems to mean the body's natural frequency (since this frequency corresponds to resonance); but I've just seen a question on my physics textbook of a pendulum oscillating at a frequency, *f*, under forced vibration and the solution used that frequency as the 'resonant frequency' in the Q factor equation to calculate the Q factor of the system.