The concept, advocated by Fred Reichheld, is that a simple measure of whether clients would be willing to refer others to your business can indicate its overall health -- and that measures to induce changes both to increase the number of enthusiastic supporters and reduce the number of unhappy client detractors will pay off in growth and success.
The question is simple enough:
How likely are you to recommend (name of your business or organization) to a colleague or friend?
Customers who respond to the survey answer this question on a one to 10 scale, with one representing total dissatisfaction, with 10 representing enthusiastic recommendation. For NPS, nines and 10s are counted as promoters (P), while answers six and under are regarded ad detractors (D). The more promoters and the fewer detractors, advocates Reichheld.
Bain and Company's website explains the concept further: