What is User Experience (UX)?
User experience is the totality of how it feels to use the product — findability, speed, clarity, error recovery, trust — engineered through research, prototyping, and usability testing rather than decorated on at the end. UX is not UI: the interface is the surface; the experience is the journey through it.
In agile delivery, UX runs one step ahead of the sprints (discovery and prototypes feeding the backlog) and one step behind (usability findings feeding rework) — a dual-track rhythm, not a phase.
Worked example
An insurance app's claim-filing flow is functionally complete and abandoned by 60% of users at the photo-upload step. Usability testing (five users, one afternoon) finds it: the upload spinner gives no progress and people assume it froze. A progress bar and a "we've got it" confirmation — two days of work — cut abandonment to 15%. Nothing in the requirements was violated by the bad version. That's what makes UX its own discipline.