Capacitor
A capacitor is an energy-storing device. It consists of two plates of conducting material. The conducting materials are sandwiched around an insulator made of, for instance, ceramic, film, glass, or air. (Hence the names ceramic condenser, film condenser, etc.). The insulator is also known as a dielectric, and it boosts a capacitor’s charging capacity.
In condenser microphones, the dielectric is air. One of the backplates and the diaphragm form the capacitor.
Capacitors and batteries both store energy. While batteries release energy gradually, capacitors discharge it quickly.