- The quality of being eccentric or odd; any eccentric behaviour.
- (mathematics) The ratio, constant for any particular conic section, of the distance of a point from the focus to its distance from the directrix.
- For an ellipse, the eccentricity is the ratio of the distance from the center to a focus divided by the length of the semi-major axis.
- (astronomy) The distance of the centre of a planet's orbit from the centre of the sun.
the quality of being eccentric
a ratio between distances in a conic section