>That's only the definition for frequences used in radio transmission, as defined by the ITU
That is both excessive and superfluous all the time the title is Fast Radio Burst. It is clear we are far from gamma rays. The real question is high or low within the radio bands and as it was pointed out above UHF is a perfectly good and more precise term than "low."
Also, the ITU regulates radio astronomy bands, defining what bands are protected where you are not allowed to operate a transmitter, even outside protected radio areas.