Why A capacitor stores energy in the electric field between two conductive plates separated by an insulator, and capacitance is the measure of how much charge it holds per volt applied. The unit is the farad (F), though practical values are usually microfarads or picofarads. The companion property, inductance, stores energy in a magnetic field instead.
Watch out Inductance is the tempting opposite: it also stores energy, but in a magnetic field created by current flowing through a coil, not in an electric field between plates.
Capacitor = electriC field; inductor = magnetic field. Match the C's.