A farad is the unit of electrical capacitance in the International System of Units (SI). It measures a capacitor's ability to store an electric charge. One farad is defined as the capacitance of a capacitor that stores one coulomb of charge at a potential difference of one volt. Capacitance is crucial in various electronic devices, such as capacitors, which are used in circuits to smooth out voltage fluctuations and store energy. The farad is a large unit, so capacitors are often rated in microfarads (µF) or picofarads (pF) for practical applications.