LF stands for low frequency and covers 30 kHz to 300 kHz in the RF range. In Europe there are many radio stations broadcasting between 150 and 250 kHz. In the US LF is used by the Navy, WWVB, and a group of radio enthusiasts who call themselves LowFers.
LowFers operate with one watt of power and are limited to a 15 meter antenna. They are able to communicate over very long distances in the LF band.