Electret is a solid dielectric with a permanent electric field. Electret is an abbreviation for ELECTRic magnET( electret is the electrical equivalent to a magnet)

In production of electret the material is melted and subjected to an electric field. The material is then cooled while still in the electric field. It will retain the charge it got(similar to a magnet that will retain the magnetic field it was subjected to) nearly infinitely.

Electret is mostly used in cheaper electrostatic headphones and electret condenser microphones.