The three things that Gladwell says you must have for job satisfaction are autonomy, complexity, and a connection between effort and reward.
According to Gladwell, work that fulfills these three criteria is meaningful. He cites teaching as an example, as well as being a physician or an entrepreneur. What matters in all of these jobs is not the money that can be earned from them, but the satisfaction they bring. And they bring satisfaction because they give autonomy, complexity, and a connection between effort and reward.
To illustrate his example, Gladwell asks us to consider whether we would rather work in a tollbooth for $100,000 a year for the rest of our lives or as an architect for $75,000 a year. He's fairly confident that most of us would choose to be an architect because it fulfills all three of his criteria for job satisfaction, and that's worth a lot more to most people than just money.