What is "pseudo-octave"

n. (context music English) An interval whose frequency ratio is not 2:1 (that of the octave), but is perceived or treated as equivalent to this ratio, and whose pitches are considered equivalent to each other as with octave equivalency.

A pseudo-octave, pseudooctave, or paradoxical octave in music is an interval whose frequency ratio is not 2:1 (2.3:1 or 1.9:1, for example), that of the octave, but is perceived or treated as equivalent to this ratio, and whose pitches are considered equivalent to each other as with octave equivalency. When used as a basis for an equal temperament, the pseudo-octave may also be called the interval of equivalence (IoE), the repeat ratio, and the nonoctave.