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Freebase(5.00 / 1 vote)Rate this definition: Electret. Electret 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.
Define accretion disk: a disk of usually gaseous matter surrounding a massive celestial object (such as a black hole) in which the matter graduallyâ¦ a disk of usually gaseous matter surrounding a massive celestial object (such as a black hole) in which the matter gradually spirals in towardâ¦