You can't be in business today without knowing about Net Promoter Score or NPS. What is NPS?
For that you can turn to Wikipedia.
You derive NPS from asking customers:
How likely is it that you would recommend our company/product/service to a friend or colleague? With the scoring of the answer most often based on a 0 to 10 scale. "Promoters" give a 9 or 10. "Passives" give a score of 7 or 8. "Detractors" give a score of 0 to 6.
To calculate NPS you take the percentage of customers who are Promoters and subtract the percentage who are Detractors.
Contrary to some popular misconceptions, NPS is meant to measure customer loyalty, not satisfaction.