Electrostatic Microphone is the strictly technical classification for what the audio industry universally calls a Capacitor or Condenser Microphone. The term describes the underlying physics of the transducer, which relies on an electrostatic charge held across two conductive plates separated by an insulator (air).

The cross-reference to "Capacitor Microphone" highlights that these terms are synonymous. "Condenser" is actually an obsolete electrical term for a capacitor, yet it has remained the standard terminology for microphones since the early 20th century. Therefore, while you will rarely see a product sold as an "electrostatic microphone," this term accurately describes the entire family of transducers (including high-end measurement mics and electrets) that convert sound into electricity through variable capacitance.