noun
oblateness; flattening
Technical term in geometry and astronomy for the degree to which a spheroid is flattened at the poles.
地球の扁平率は約1/298です。
The Earth's oblateness is about 1/298.
Compound of 扁平 (へんぺい, 'flat, oblate') and 率 (りつ, 'rate, ratio').