Net Promoter Score (NPS) is a metric for measuring customer satisfaction and loyalty by subtracting the percentage of customers who are detractors from the percentage who are promoters. Companies with higher NPS scores grow faster than competitors. The NPS system categorizes customers as promoters, passives, or detractors based on their response to a key question about how likely they are to recommend the company. Tracking NPS provides insights into why customers feel the way they do and helps companies improve customer relationships and growth. Companies with the most efficient growth engines like Amazon and Costco have NPS ratings of 50-80%, showing there is always room for improvement.