What type of electrical component consists of conductive surfaces separated by an insulator?

A capacitor is a fundamental electronic component designed to store electrical energy in an electric field. It is physically constructed using two or more conductive plates, or surfaces, separated by a non-conductive dielectric material which acts as the insulator. When voltage is applied across these plates, an electric field builds up across the insulator, allowing it to store energy. This is entirely different from a resistor, which dissipates energy as heat, or a potentiometer, which is simply an adjustable resistor. An oscillator is a complete electrical circuit used to generate a repeating signal, not a basic passive component. Therefore, the capacitor is the only correct component matching this specific physical description.