anomaly

An anomaly is something that doesn't fit with what's expected or normal.

You might hear people talk about anomalies in science, like when an experiment produces results that don't match what scientists thought would happen. Or maybe someone says they found an anomaly in their tax return – a mistake that changed the amount of money they owe. Sometimes you'll see "anomaly" used to describe something strange or unexpected, even if it's not necessarily bad. For example, a city might have an anomaly when it comes to traffic patterns, with more cars traveling through one area than others at different times of day.