An anomaly is any occurrence or object that is strange, unusual, or unique. It can also mean a discrepancy or deviation from an established rule or trend.

Anomalistics is the study of scientific anomalies. In computer science, anomaly detection refers to the process of detecting anomalies from the relevant data.

In the following particular contexts, "anomaly" may refer to:

Astronomy and Celestial Mechanics

In astronomy, an anomaly is a quantity measured with respect to an apsis, usually the periapsis. Similarly, "anomalous" is synonymous with "apsidal".

• Eccentric anomaly, intermediate value used to compute the position of a celestial object as a function of time
• Flyby anomaly, unexpected energy increase during Earth flybys of satellites
• Mean anomaly, measure of time in the study of orbital dynamics
• Pioneer anomaly, observed deviation of the trajectories of various unmanned spacecraft
• South Atlantic Anomaly, region where Earth's inner van Allen radiation belt makes its closest approach to the planet's surface
• True anomaly, angle between the direction of periapsis and the current position of an object on its orbit.
• Anomalous precession, another term for apsidal precession.