The cutoff frequency is a characteristic value of frequency-dependent quadrupoles. This applies to passive components such as analogfilters, high-pass, low-pass and band-pass filters, but also to active components such as amplifiers, microphones or loudspeakers.
The cutoff frequency is the frequency at which the level drop is 3 dB compared to the level in a straight frequency response. This corresponds to the voltage value of 0.707 referred to the highest voltage value and thus a voltage reduction of 41%.
The cutoff frequency refers equally to the frequency at the lower -3 dB value, i.e. the lower cutoff frequency, and the upper -3 dB value, i.e. the upper cutoff frequency. The difference between the two frequencies is the bandwidth.