In practice
Measure it with behaviour rather than opinion: task completion, drop-off by step, and the queries that end in a return to search.
Test on a mid-range phone on a normal connection — that is the experience most visitors actually have.
Why it matters
Search engines increasingly model satisfaction, so experience and ranking have stopped being separate conversations.
It is also the shared ground where SEO, design and product work on the same problem instead of trading blame.
Related terms