A long range hyperbolic, continuous wave phase comparison system of navigation employing three or more phase locked stations to generate two or more patterns of lines of position.
It operates in the very low frequency band, near 10 kHz, where propagation via the lower ionosphere is characteristically of great range and of a predictable degree of stability, both day and night.
The baseline between the two stations required to generate a single set of hyperbolic co-ordinates is typically 3 to 5 thousand miles long. The fix accuracy is moderate but may be improved in limited areas by certain techniques.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM