What does "cut-off frequency" refer to?

Cut-off frequency refers to the specific point in a filter's frequency response where the output signal power begins to drop significantly compared to the input signal. At this frequency, the output typically falls to a defined level, often set at 3 dB below the maximum output level. This concept is crucial in understanding how filters operate, as it defines the boundary between the passband (where signals are allowed to pass through) and the stopband (where signals are attenuated).

When designing filters, knowing the cut-off frequency helps in determining how the circuit will behave with varying frequencies, impacting the performance of audio equipment, communication systems, and many other applications in electronics. By understanding this point, engineers can better tailor the filter to meet specific needs, ensuring signal integrity within the desired range while attenuating unwanted frequencies outside of that range.