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extremely low frequency

noun Radio.
  1. any frequency between 30 and 300 hertz. Abbreviation: ELF, elf

Origin of extremely low frequency

First recorded in 1965–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for extremely low frequency

extremely low frequency

noun
  1. a radio frequency or radio-frequency band below 3 kilohertzAbbreviation: ELF
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012