An outlier is something that stands apart from all the others in a group because it's surprisingly different. In math class, if most students score between 75 and 85 on a test, but one student scores 40 and another scores 100, those two scores are outliers: they fall far outside the normal range.

Scientists and mathematicians pay special attention to outliers because they can reveal important information. Sometimes an outlier signals a mistake, like when you accidentally write down the wrong number while collecting data. But sometimes an outlier points to something genuinely unusual and worth investigating. If nine seeds planted in identical conditions grow to about six inches tall but one grows to two feet, that outlier plant might have a special genetic trait worth studying.

The word also describes people whose abilities or circumstances set them dramatically apart from others. A twelve-year-old who composes symphonies or a basketball player who's a foot taller than everyone else on the court would be an outlier. Being an outlier isn't automatically good or bad; it simply means standing far outside the normal pattern. Understanding outliers helps us see both what's typical and what's exceptional.