End user is the consumer who receive and use a product or service after going through all the tests and modifications. They are possibly the final part of the process of development of the product and they are fundamental to this process. The saying that an unsatisfied end user seldom buys products goes a long way into showing that the product will not perform well in the market if the user is not satisfied.
Final customer may have or may not have different traits depending on the type of good or service used. For instance, if the software is for business use then the end user would be a businessman and the idea, skills and experience of such an individual should inform the layout of the software as well as its features. Defining the end user at the start of the project helps in getting closer and deciding what is good for the end user hence developing good end user oriented product of service.