The frequency range (or ranges) outside the passband of the filter where attenuation of signal is desirable. This region is normally specified at some attenuation value or values. The closer to the passband that attenuation is specified, the more complex the filter design becomes.

The area of frequency where it is desirable to reject or attenuate all signals, as much as is practical.

The part of the frequency spectrum that is subjected to specified attenuation of signal strength by a filter.

The frequency range of a band reject filter which has high insertion loss and therefore stops signals from passing. A stopband is defined by identifying its upper and lower frequency.

A wavelength interval used to denote a spectral region of energy that is not transmitted by a filter.

A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through. Frequencies between the lower and upper limits are not transmitted.