A digital filter is a mathematical algorithm used to process digital signals, enhancing or suppressing certain frequencies. It converts an input signal into an output signal by applying specific rules, allowing for the removal of unwanted noise or the emphasis of desired features. Digital filters are widely used in various applications, including audio processing, telecommunications, and image enhancement. There are two main types of digital filters: FIR (Finite Impulse Response) and IIR (Infinite Impulse Response). FIR filters are known for their stability and linear phase response, while IIR filters are more efficient in terms of computation but can be less stable. Both types play crucial roles in modern signal processing systems.