Definition
An Outlier is an observation that differs substantially from other values in a dataset.
Human Explanation
It is a result that lies noticeably outside the pattern formed by most other observations.
Why it Matters
Outliers may indicate measurement errors, unusual events or important information requiring further investigation. They can also materially affect statistical summaries and models.
Conceptual Boundary
An Outlier is not automatically an error. It may represent a genuine but rare event, and whether a value is unusual depends on context and the method used to identify it.
Practical Perspective
Before removing an Outlier, investigate its origin, document the decision and evaluate how retaining or excluding it changes the analysis.