anomalous

Anomalous is an adjective used to describe something that deviates from what is standard, expected, or typical. In everyday language it often signals something unusual, unexpected, or difficult to explain. In scientific discourse, the term is used to flag observations, measurements, or phenomena that do not conform to established models or norms.

Etymology: The word comes from Latin anomalus, from Greek anomalos meaning irregular. It is formed from a- meaning not and homalos meaning even or regular.

Usage in science and mathematics: In physics and chemistry, an anomalous result may prompt re-examination of assumptions. Notable examples include the anomalous magnetic moment of the electron, a measured quantity that deviates from the simple Dirac prediction and is explained by quantum corrections. In mathematics, an anomalous diffusion describes transport that violates the linear relation between time and mean squared displacement that holds for ordinary diffusion.

In statistics and data analysis, anomalous observations are outliers. Anomaly detection is the field that seeks to identify such observations for quality control, fraud detection, or safety applications.

In other domains, anomalies may indicate rare variants, measurement error, or new phenomena. The label is typically neutral, indicating deviation rather than value judgment; whether an anomaly is interesting or problematic depends on context.