Wiktionary
n. (context physics English) A solid dielectric having a quasi-permanent charge; usually a metallized film; used in electroacoustic and electromechanical transducers and in air filters.
Wikipedia
Electret (formed of elektr- from " electricity" and -et from " magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Oliver Heaviside coined this term in 1885. Materials with electret properties were, however, already studied since the early 18th century. One particular example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate. The electrophorus was originally invented by Johan Carl Wilcke in Sweden and again by Alessandro Volta in Italy.
Usage examples of "electret".
It had a Van de Graaff generator, spark gaps, and a battery of electrets.
Koltukhov, whose electret scheme was being applied, had now become just about the most enthusiastic champion of a pipeless oil pipeline.
They must have had some excellent resins, which they turned into highly charged electrets.
Fedor Matveyev mentioned those resins, leading Koltukhov to conceive the idea of powerfully charged electrets.