IIR2, or Infinite Impulse Response Filter 2, is a type of digital filter used in signal processing that utilizes feedback to achieve desired frequency response characteristics. It allows for more efficient design and implementation compared to FIR (Finite Impulse Response) filters, particularly in applications requiring complex filtering. IIR2 filters can achieve sharp roll-offs and better performance with fewer coefficients but may introduce stability and phase distortion issues. They are commonly used in audio processing, telecommunications, and control systems.