(1) The act of attenuating. (2) Diminution of virulence in a strain of an organism, obtained through selection of variants that occur naturally or through experimental means. (3) Loss of energy of a beam of radiant, ultrasound, or other energy because of absorption, scattering, beam divergence, and other causes as the beam propagates through a medium. (4) Regulation of termination of transcription; involved in control of gene expression in specific tissues.