The unit typically used to indicate the slope of a filter, or how fast the frequency response rolls off past the cutoff frequency. Example: A 24 dB/octave filter would attenuate an input signal by 24 dB one octave above the cutoff frequency, by 48 dB two octaves above the cutoff frequency, and so on.

In electronics, an octave (symbol oct) is a logarithmic unit for ratios between frequencies, with one octave corresponding to a doubling of frequency. For example, the frequency one octave above 40 Hz is 80 Hz. The term is derived from the Western musical scale where an octave is a doubling in frequency. Specification in terms of octaves is therefore common in audio electronics.

Along with the decade, it is a unit used to describe frequency bands or frequency ratios.