An RC filter is an electronic circuit that uses a resistor (R) and a capacitor (C) to filter signals. It can be designed to allow certain frequencies to pass while blocking others, making it useful in various applications like audio processing and signal conditioning. There are two main types: low-pass filters, which let low frequencies through and block high frequencies, and high-pass filters, which do the opposite. The behavior of an RC filter is determined by the values of the resistor and capacitor. The cutoff frequency, where the filter starts to attenuate signals, is calculated using these values. This makes RC filters essential in designing circuits for specific frequency responses.