NPS (Net Promoter Score): a customer-loyalty number from minus 100 to plus 100, calculated by subtracting the share of detractors (0 to 6 on a 0-10 scale) from the share of promoters (9 or 10).
Reichheld, a Bain consultant, argued in "The One Number You Need to Grow" that a single survey question ("How likely are you to recommend us?") predicted revenue growth better than complex satisfaction surveys. The article spread quickly through Fortune 500 boardrooms, and within a decade NPS was a standard line item in shareholder letters from GE to Apple.