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Low frequency radio astronomy (or LF radio astronomy) obviously refers to the use of the lower frequency portion of radio, but the term is not consistently used regarding a threshold: I find various radio-astronomy groups cite differing thresholds. 350 MHz, or something in that region seems common: in other words, essentially everything lower-frequency than microwave, which includes much of what is termed radio astronomy. For example, the Low-frequency Array senses up to 240 MHz. But the term has also been used specifically for the lower-frequency end of this wide range: I've seen 30 MHz cited as the upper threshold, which is not far above the low-frequency end of the radio atmospheric window; an upper-threshold much lower than this would imply the need for a space observatory.
In contrast to this, for regulation and communications purposes, the ITU uses the terms high frequency and low frequency for specific communications bands that are far different than the typical language of radio astronomy, though astronomers clearly must refer to these ITU bands on occasion. Some of the ITU bands:
| Very low frequency | VLF | 3-30 kHz |
| Low frequency | LF | 30-300 kHz |
| Medium frequency | MF | 300-3000 kHz |
| High frequency | HF | 3-30 MHz |
| Very high frequency | VHF | 30-300 MHz |