Anomaly

Deviation from the common rule; an irregularity; anything anomalous.

The angular distance of a planet from its perihelion, as seen from the sun. This is the true anomaly. The eccentric anomaly is a corresponding angle at the center of the elliptic orbit of the planet. The mean anomaly is what the anomaly would be if the planet's angular motion were uniform.

The angle measuring apparent irregularities in the motion of a planet.

Any deviation from the essential characteristics of a specific type.

(astronomy) position of a planet as defined by its angular distance from its perihelion (as observed from the sun)

deviation from the normal or common order or form or rule