We toss around the term "user experience" (UX) a lot, mostly as a shorthand for something like "where industrial design meets interface design." But to be perfectly honest, that tendency does this branch of design very little justice.
The Disciplines of User Experience Design is a mega Venn diagram by Dan Saffer (given a pretty makeover by Thomas Gläser) that explores all of the overlap between UX and other fields of design. You’ll see UX’s overlap with architecture, human factors, sound design, and computer science—and you’ll also see its sweet spot, interaction design, with user interface and all of its tentacles at its heart.
To be fair, it’s impossible to present a thesis on design like this without inviting the Internet masses to scrutinize its organization. As one commenter pointed out, where is service design in this mix? Meanwhile, I wondered how "psychology" or "cognitive science" can possibly be outside of the realm of UX, as understanding user thought process and cognitive loads are two massively important parts of the field. And how come sound has no place in the "interaction design" sweet spot? Can interactions only be visual in nature? Of course not.
But to critique a piece like this is to ungratefully overlook its utility: Don’t see this as the only road map for the entire UX design industry, but a postulation as to why it’s so darned complicated to nail good UX. To think anyone could be an expert in each of these circles is sheer absurdity. Scratch that: To think any designer could be an expert in each of these circles is sheer absurdity, but to recognize that every end user is an expert in each of these circles is highly important. As humans and end users, we might not know what makes an experience right, but we certainly know when it’s wrong.