Just dumping my thoughts from a recent discussion…
You have something that you want your users to do. It could be signing up for your product, giving you their contact number, getting more productive using your product, or clicking on a particular button inside your app. How do you make them do this?
I’d like to quote a favorite statesman of mine in the domain of public policy design:
If you want people to do good, you need to make it easy to do good, and extremely hard to do bad things.
The idea is that most people tend to do what is convenient for them at the moment, without objectively weighing the pros and cons. So if you make it convenient for them to do good, most of them will do it. You can deal with the outliers by imposing penalties.
Now coming back to the original question, UX design is through which you make the users do what is desired. Applying the public-policy funda to UX design, a good user experience is something which makes it easy for your users to do what is desired.
All the aspects of good UX design – being intuitive, less number of clicks, etc – can be derived from this.