Band-stop filter

In electronics, a band-stop filter is a filter that attenuates, usually to very low levels, all frequencies between two non-zero, finite limits and passes all frequencies not within the limits. It is mostly called notch filter, which is the opposite of a band-pass filter.

Note: A band-stop filter may be designed to stop the specified band of frequencies but usually only attenuates them below some specified level.

Synonyms band-elimination filter, band-rejection filter, band-suppression filter, notched filter.

Source: from Federal Standard 1037C and from MIL-STD-188