lower or upper limiting frequency of a pass-band or stop-bandfrequency at which the magnitude of a measured characteristic quantity has decreased to a specified fraction of its low-frequency value NOTE - For a transistor, the cut-off frequency usually applies to the small-signal short-circuit forward current transfer ratio for either the common-base or common-emitter configuration.a frequency of the pass band at which the relative attenuation of a piezoelectric filter reaches a specified valuethe lowest frequency above which a radio wave is able to penetrate an ionospheric layer at the angle of incidence required to establish transmission between specified points by reflection from a higher layer NOTE - In the case of vertical incidence, the cut-off frequency is also called the blanketing frequency.