Short definition
UX is the discipline of designing how a person feels and what they can do when they use a product, with the goal of making the desired action effortless.
In depth
User experience covers everything from information architecture and interaction design to copy, accessibility, and performance. On a service-business website, UX is the difference between a visitor finding the phone number in two seconds versus three frustrated taps. UX is measured with conversion rate, task success rate, time-to-action, and satisfaction (NPS, CSAT). It overlaps with CRO but is broader — UX includes post-conversion experiences (booking, onboarding) where CRO usually stops at the conversion event.
Example
A roofing site redesigns its mobile nav so the phone CTA is visible on every screen. Time-to-call drops from 47 to 12 seconds and call volume rises 31%.