terminology - What does "end-user" mean?

UX folks like to talk of the "end user" (examples in 1 2 3), because that is whom they are advocating for. However, the term is somewhat ambiguous: assuming I write an UI library, is the end-user the programmer who uses the library, or the person which uses the product which, in turn, uses the library?

I'm also asking the question because, as far as I know, Human-Machine-Interaction was initially developed for pilots during the 2nd world war, where the term "end-user" seems misplaced.

So is there a good definition of end-user within the context of UX/Usability? Or some historical context why this term came up, which point it tries to make?

Answer

The end-user is a tricky term which has a variety of meanings depending on when and where it's used.

Whereas in economics the end-user is the person who uses the product, in contracts this term usually refers to the non-reseller, who does not necessarily consume the product at all.

For example, if Cheesecake Inc. sells cookies to your grandmother, who then brings them to you, and you eat them, the end-user would refer to you in economics, but to the grandmother in most contracts.

In UX design, the term refers to the former, and so it's you who the baker would have to take into consideration when designing the cookie. However, for the designer of the cookie packaging—considering that you grandmother takes the cookies out of the packaging before presenting them to you—, the end-user may very well be the grandmother.

When it comes to UI libraries and similar content, the question becomes that much more difficult and really has no one correct answer. Like in the cookie/packaging example above, I'd divide your UI library product into two imaginary parts, one of which will have the programmer as the end-user, and the other the user of their creation.

For instance, the code and APIs of the UI library will only ever be used by the programmer. He is thus the end-user of this part of the product, and should be the one you take into consideration when designing the product. On the other hand, the presentation of the individual UI components will be used by someone else, and so the end-user of this part of the product is that someone who will use the final product of the aforementioned programmer.