A cutoff frequency is a frequency boundary in a system's frequency response at which the power level is greater or less than a given fixed value.
In electrical engineering, cutoff frequency or corner frequency is the frequency either above or below which the power output of a circuit, such as a line, amplifier, or electronic filter has fallen or risen to a given proportion of the power in the passband. Most frequently this proportion is half the passband power, also referred to as the 3 dB point since a fall of 3 dB corresponds approximately to half power.
