V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

IIR
       Infinite Impulse Response (DSP)


The Free On-line Dictionary of Computing (30 December 2018):

Infinite Impulse Response
IIR

    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)