IIR

from The Free On-line Dictionary of Computing (8 July 2008)

Infinite Impulse Response
IIR

   <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)