f region Fregatidae • freibergite · · · Info · Definitions · Characters · · f region · · Text Common · · Latin · · Scripts 8 · · Length 3 · · Syllables Definitions · · · (noun) the highest region of the ionosphere (from 90 to 600 miles up) which contains the highest concentration of free electrons and is most useful for long-range radio transmission. Synonyms: Appleton layer, F layer, F region. · · Noun Definition 1 Characters · · space U+0020 e latin small letter e U+0065 f latin small letter f U+0066 g latin small letter g U+0067 i latin small letter i U+0069 n latin small letter n U+006E o latin small letter o U+006F r latin small letter r U+0072