Malcolm Gladwell begins the introduction of his nonfiction best-selling book Outliers: The Story of Success with an abridged version of a definition of "outlier" found in the Merriam-Webster Dictionary:

out·li·er noun

1: something that is situated away from or classed differently from a main or related body

2: a statistical observation that is markedly different in value from the others of the sample.

Gladwell uses the dictionary definition of "outlier" to establish the premise of his book, which is that Gladwell believes there is an explanation for why some people achieve unusual and even extraordinary success in their personal endeavors that lies outside the realm of normal, recognizable experience.

In the context of the book, in chapter 1, "The Matthew Effect," Gladwell defines "outliers" as "men and women who do things that are out of the ordinary" and amends that definition to include people who "in a particular field reached their lofty status through a combination of ability, opportunity, and utterly arbitrary advantage."

In chapter 2, "The 10,000-Hour Rule," Gladwell adds that "outliers" are "beneficiaries of some kind of unusual opportunity" and those who benefit from "hidden opportunities."

In chapter 5, "The Three Lessons of Joe Flom," Gladwell expands on the idea of "hidden opportunities." He contends that "outliers always have help along the way," that "outliers" are "products of particular places and environments," that "outliers" often suffer setbacks, and that "buried in that setback was a golden opportunity."

In chapter 6, "Harlan, Kentucky," Gladwell summarizes part 1 of the book:

So far in Outliers we've seen that success arises out of the steady accumulation of advantages: when and where you are born, what your parents did for a living, and what the circumstances of your upbringing were all make a significant difference in how well you do in the world.

In part 2, chapter 9, "Marita's Bargain," Gladwell returns once again to the concept of "opportunities," and he observes that "success follows a predictable course" and that "outliers" are those "who have been given opportunities—and who have had the strength and presence of mind to seize them."

Nevertheless, when all the aspects of what Gladwell defines an "outlier" to be are considered, Gladwell himself concludes,

[Outliers] are products of history and community, of opportunity and legacy. Their success is not exceptional or mysterious. It is grounded in a web of advantages and inheritances, some deserved, some not, some earned, some just plain lucky—but all critical to making them who they are. The outlier, in the end, is not an outlier at all.