Revision Standard - Superseded. Superseded by 549-2005 (SH/SS95331). This standard defines terms related to the areas of corona and the electromagnetic environment of overhead power lines. Its scope is to define the most widely used terms specific to or associated with overhead power-line corona and fields. This includes terms used in electric and magnetic fields, ions, radio frequency propagation, electromagnetic signals and noise, audible noise, coupled voltages and current, shock and perception, weather and related statistical terms, and measurements and measuring devices.