An end user is the person that ultimately uses a piece of software or hardware. They are the last person at the end of the product development process after it has been designed, developed, tested, and delivered. Good product designers consider their needs during product development to create something they'll find helpful and pleasant to use.
A product's end user is typically uninvolved in the development process, and in many cases, they are uninvolved in its administration and maintenance as well. However, some developers reach out and recruit some of their end users to help in the development process as beta testers. Beta testing allows some end users to use an early version of the product as they normally would, helping the developer find bugs while providing suggestions to improve the user experience.
The end user is not always the product's customer, especially when it comes to business software. The person responsible for purchasing decisions is often in a different role than the people who will be using it regularly. A product might also have several different kinds of end user to consider. For example, an e-learning platform's end users consist of the instructors creating and teaching the material and the users taking the lessons, while the customer is the company's training manager who makes the purchasing decision. IT staff, meanwhile, administer and support the software but are not end users.