Finite Impulse Response: A class of filter designs whose impulse response falls to zero in a predictable, finite length of time, as opposed to an IIR (Infinite Impulse Response) design whose impulse response may never fully attenuate the impulse. A common use of FIR is to produce filters with a linear phase response. Filters such as analog anti-aliasing filters which have a very sharp rolloff slope produce unacceptable amounts of phase distortion in the output signal; FIR filters are used at the end of an oversampling A/D chain to eliminate any signal that would represent aliasing in the slower output datastream, without causing significant phase distortion.