In general, an octave is a frequency interval where the upper cutoff frequency has twice the value of the lower cutoff frequency. This applies to all frequency ranges, from audio frequencies up to microwaves.
In music, an octave is a musical interval where the upper note has twice the frequency of the lower note. Thus, the concert pitch a` has a frequency of 440 Hz, the a'', which is an octave higher, has one of 880 Hz, and the a''' has a frequency of 1.760 kHz.
In terms of frequency, an octave is a range of frequencies between a lower frequency and an upper frequency, which are in the ratio 1:2. The center frequency of an octave is calculated from the geometric mean of both frequencies. The standardized center frequencies are 16 Hz, 32 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, and 16 kHz. An octave consists of three thirds or 6 whole tones, 12 semitones, 24 quarter tones. A semitone, in turn, consists of 100 cents.