Back Electret is a type of condenser (or capacitor) microphone that uses a material with a permanent electrical charge.

In a traditional condenser microphone, an external voltage (phantom power) is needed to polarize the capsule (maintain the electrical charge between the diaphragm and the backplate).

In the back electret design, the backplate, which is fixed behind the diaphragm, is made of a material that has a permanent electrical charge (the electret).

This simplifies the construction of the microphone, as it eliminates the need for an external voltage to Polarize the capsule. Phantom power is still needed, but only to power the microphone's small internal preamplifier (FET circuit). This technology has enabled the creation of high-quality, cheaper, more robust, and miniature condenser microphones, which are very common in lavalier microphones, instrument microphones, and many modern studio models.