IIR stands for infinite impulse response, IIR filter is one of the two primary types of digital filter. It is a very important part of a digital signal processing application. The impulse response of the IIR filter is to be infinite because of feedback in the filter; If you put in an impulse an infinite number of non zero values will come out.
IIR filter is that it can achieve a given filtering characteristic using fewer calculations and memory than a similar FIR filter.
One of the disadvantages of IIR filter is harder to implement using fix point arithmetic also don't offer the computational advantages of FIR filters for multi-rate applications.