How much complexity is needed to make it simple?
Of course, it is not a brand new word, you can find several different uses mostly since 2004, but I would like to relate it with interaction.

Think about the surface of the Audi A5 bodywork: at a glance, it seems to be simple. Let's say it is a very clean or neat design; but try to reproduce it, to draw it from different points of view.

How to face complexity making it apparently simple? Sometimes it is trivial: just hide it, like in the mechanism of a clock watch. Some other times you have to think a lot, experiment a lot, and build a lot of knowledge. When you slide the initial switch of an iphone to start operating, you feel it simple, but a very complex feedback is taking place. I am not speaking about thousands of software lines, I just say that the movement that make you feel this switch (slide) real - the way it react, come back if you do not end the finger movement, end its own track, etc. - is not simple at all. That is what I mean when I say simplexity. It is not just a matter of usability, not just ergonomic nor metaphor, it is all of them plus comfort,  

As Sandee Brawarsky wrote, simplexity is also a growing genre on nonfiction books half way between psichology, economics and decision making. Is in that context where the best seller from Jeffrey Kluger "Simplexity" take the neologism to explain why some simple things become complex and complex things can be made simple. Very interesting but not the same idea I mean above.

Also Renault have used the word to refer a concept truck five years ago