When amplitude is changed by combining two or more waves or cycles of different amplitudes.
The input-to-output reduction imposed by the filter upon an input signal.
In physics, attenuation (in some contexts also called extinction) is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.
In electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, as well as in air (radio waves). (wikipedia)
The maximum attenuation a filter can apply at a specific frequency, bounded by electrical noise, parasitics and other non-ideal filter characteristics.