anharmonic ratio; cross ratio
Technical term in projective geometry; refers to the ratio of ratios of distances among four collinear points.
In projective geometry, the cross ratio is a fundamental invariant.
Compound of 非 (hi, 'non-') + 調和 (chōwa, 'harmony') + 比 (hi, 'ratio'), literally 'non-harmonic ratio'. The term is a direct translation of the English 'anharmonic ratio'.