A Butterworth filter is an electronic filter designed to have a flat frequency response in the passband, meaning it allows signals to pass through without distortion. It is characterized by a smooth transition from the passband to the stopband, making it ideal for applications where signal integrity is crucial. The filter's design can be implemented in various forms, including analog and digital circuits. The order of a Butterworth filter determines how quickly the filter attenuates signals outside the passband. Higher-order filters provide steeper roll-off, which means they can more effectively block unwanted frequencies. Butterworth filters are commonly used in audio processing, communication systems, and other applications requiring precise frequency control.