In December 2003 Fred Reichheld of Bain & Company published “The One Number You Need to Grow” in Harvard Business Review. The number came from one question: “How likely is it that you would recommend [company X] to a friend or colleague?”
Customers who answer 9 or 10 are promoters. Those who answer 6 or lower are detractors. The share of detractors is subtracted from the share of promoters, and the result is the Net Promoter Score. According to Wikipedia, versions of it were used by two-thirds of Fortune 1000 companies by 2020.
Researchers have questioned the claim behind the score. They found “no empirical evidence” that the question predicts growth better than other questions.