Customer service is the service or care that a consumer receives before, during and after a purchase. It’s one of the factors that come in to play when a consumer is determining buying value, the other is the quality of the product or service that is being offered. Consumers often must encounter an experience to not only be a satisfied customer, but a loyal customer. Customer service is a part of that experience.

source:
http://marketing.about.com/od/plantutorialsandsamples/a/What-Is-Customer-Service.htm