The farad is the SI unit of electrical capacitance.
A capacitor has a capacitance of one farad when a potential difference of one volt creates a stored charge of one coulomb. The farad is therefore defined by the relationship C = Q/V, where C is capacitance, Q is charge, and V is voltage.
The unit honors English physicist Michael Faraday, whose work in electromagnetism helped establish the relationship between electricity and magnetism. One farad is a very large capacitance for many ordinary circuits, so components are commonly labeled in microfarads, nanofarads, or picofarads.
Capacitors store energy in an electric field between conductors. They are used for filtering, timing, signal coupling, and temporary energy storage. Capacitance is not the same as resistance: resistance opposes current, whereas capacitance describes how much charge can be stored for a given voltage.