>Net Promoter or Net Promoter Score (NPS) is a management tool that can be used to gauge the loyalty of a firm's customer relationships. It serves as an alternative to traditional customer satisfaction research and is claimed to be correlated with revenue growth. NPS has been widely adopted with more than two thirds of Fortune 1000 companies using the metric. The tool aims to measure the loyalty that exists between a provider and a consumer. > wikipedia
This tool was developed by Fred Reichheld of Bain. He was looking for the customer research measurement that best predicted long-term revenue growth.
It is used define "customer advocacy" in a marketplace.