Extremely Low Frequency is Electromagnetic Radiation (EMR) with Wavelength defined by the ITU to be in the range of 3Hz to 30Hz. It is considered within the lower-Frequency end of the Radio spectrum, or beyond (Subradio). It is adjacent to Super Low Frequency (SLF) and Tremendously Low Frequency (TLF).
Super Low Frequency (SLF)
Tremendously Low Frequency (TLF)