What is Customer Service?

Please note that this particular post is work in progress, because honestly every day I learn something new about the wonderful world of customer service.

For example, did you know that the Philadelphia Zoo uses the following core values to build a reputation for customer service:

Listen
Empathize
Action
Problem Solve

I also recall reading an interview that summarized customer loyalty as effective customer relationship management coupled with excellent customer service. So how would you define customer service?