Slope

Most filters typically have a cutoff or corner frequency they are tuned to. It then reduces (filters) the frequency spectrum of a signal going through it so that it harmonics get progressively quieter the further away they are from this cutoff. The strength of this effect is referred to as its slope. Most filters have slopes that are defined multiples of 6 decibels (dB) weaker for each octave further away you get from the cutoff frequency. For example, a low-pass filter (LPF) with a slope of 24 dB/octave would attenuate harmonics one octave above its cutoff frequency by 24 decibels.