orbital eccentricity
Technical term used in astronomy and orbital mechanics to describe how much an orbit deviates from a perfect circle.
The larger the orbital eccentricity, the more elongated the elliptical orbit becomes.
General term for eccentricity in geometry; 軌道の離心率 specifically refers to the eccentricity of an orbit.
Compound of 軌道 (orbit) + の (possessive particle) + 離心率 (eccentricity). The term is a direct translation of the English 'orbital eccentricity'.