HF means High Frequency; VHF means Very High Frequency; and UHF means Ultra High Frequency. These are all names for different sections of a broad spectrum of radio frequencies.
The definition of the above frequencies are as follows:
(HF) or HIgh- frequency is from 3-30 MHz
(VHF) or Very HIgh Frequency is from 30-300 MHz
(UHV) or Ultra HIgh Frequency is from 300 MHz to 3 GHz
Other sections of frequencies--such as low frequency-- are not really spoken about. This is because this is not a term used for civilian radio.
When one thinks about the history of handheld ham radios for survival, it all makes sense. The thought was “this is low or this high.” Frequencies developed through the years which developed higher and higher. From low frequency (LF) to High frequency (HF), Very High Frequency (VHF) and eventually Ultra High frequency (UHF).