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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.
From Wikipedia, the free encyclopedia. Artist's conception of a binary star system with one black hole and one main sequence star. An accretion disc (or accretion disk) is an astronomical term. It describes a disc of material being drawn in by gravity to a centre of mass, such as a star or black hole. As the material comes in, it spins round the central body and radiates energy.