The term 'Unit of Capacitance' refers to the measurement of a capacitor's ability to store electrical charge. The two most common units of capacitance are the Farad (5 letters) and the Abfarad (7 letters). The Farad is the SI unit of capacitance, and is defined as the capacitance of a capacitor that stores one coulomb of charge when one volt of potential difference is applied across it. The Abfarad is an obsolete unit of capacitance, and is equal to one billionth of a Farad.