Customer Defined
From wsuwiki
It is important to know who exactly your customer is during a project. For ME416, the customer is most likely a project sponsor. Knowing your sponsor allows you to make better judgments about what is important in the design. The customer’s satisfaction with your design will ultimately be greater when you prioritize according to their needs.
In the workforce, the customer could be the marketing department, your manager, or the CEO/CFO/CEE. Most commonly, the "customer" is all of the above, and the QFD process helps keep awareness of this throughout the design of a product.