User and End-User
The user refers broadly to anyone who may use or maintain a product, and could include people such as system administrators, IT experts, and computer technicians.
The end-user is the person ultimately intended to use a product. They may not have the technical know-how or skill of the product’s administrators or designers.
For example, a medical device may have a variety of users including doctors and technicians. They may use the device for monitoring and helping patients set up their device or interpret its readings. The end-user of this medical device would be the patient who needs to interact with the interface on a regular basis. In other cases, such as deciding which web browser to use at home, the user and end-user may be the same person.