Customer
A person who defines the requirements for a service and takes responsibility for the outcomes of service consumption. The customer is the entity that pays for the service (either financially or via budget allocation).
Impact
If you don't know who your customer is, you are building in a vacuum. Misalignment between customer expectations and service delivery is the primary cause of IT failure.
Weinto take
We distinguish between the Customer (who pays) and the User (who touches the keyboard). Our job is to delight the User while solving the business problem for the Customer. Sometimes this means telling the Customer "No" when they ask for a feature that would hurt the User experience.