1. Something different, abnormal, irregular or not easily classified
2. deviation from the common rule
3. in natural science; is a persisting deviation in a physical quantity from its expected value, e.g., the systematic difference between a measurement and a trend or a model prediction
4. a person, thing or event that is far from normal
5. in astronomy, the angular distance of a planet or satellite from its last perihelion or perigee.
Etymology: Anomaly comes from the Greek word anōmalos, which means “uneven” or “irregular.” Anōmalos comes from the prefix a- (meaning “not”) and the word homalos (meaning “even”)—and homalos comes from homos. Homos in Greek means “the same.”
Summer snow, while an anomaly, is not unknown.
With the rise of bank frauds, using data to detect anomalies in credit card transactions is common.