infinite impulse response

Infinite impulse response (IIR) is a property of signal processing systems. Systems with that property are known as IIR systems or when dealing with electronic filter systems as IIR filters. They have an impulse response function which is non-zero over an infinite length of time. This is in contrast to finite impulse response filters (FIR) which have fixed-duration impulse responses. The simplest analog IIR filter is an RC filter made up of a single resistor (R) feeding into a node shared with a single capacitor (C). This filter has an exponential impulse response characterized by an RC time constant.
See more at Wikipedia.org...

<electronics, DSP> A type of digital signal filter, in which every sample of output is the weighted sum of past and current samples of input, using all past samples, but the weights of past samples are an inverse function of the sample age, approaching zero for old samples.
(2001-06-06)