NPS (Net Promoter Score) is a metric measuring customer loyalty by asking one question: "How likely are you to recommend this to others?" on a 0 to 10 scale. Scores 9 to 10 are Promoters (loyal enthusiasts), 7 to 8 are Passives (satisfied but unenthusiastic), 0 to 6 are Detractors (unhappy customers). Calculate NPS by subtracting percentage of Detractors from Promoters. Scores range from negative 100 to positive 100. Above 50 is excellent, 70+ is world class. Track NPS regularly to measure customer satisfaction trends.