Level: Basic
Usability is a component of user experience, not a synonym for it, and conflating the two leads to an incomplete view of how a site is actually performing.
Usability Is Narrowly About Task Completion
Can someone accomplish a specific goal efficiently, without errors or confusion? That's the core question usability answers.
UX Includes Emotional and Contextual Factors Too
Trust, delight, frustration, and overall impression all factor into user experience in ways a narrow usability test doesn't fully capture.
A Highly Usable Site Can Still Feel Unpleasant
A site can be technically easy to use while still feeling cold, untrustworthy, or generically unmemorable — usability alone doesn't guarantee a good overall experience.
Next step: Use the Get Source Code of Webpage to review a real page's structure to see where usability and broader experience factors might diverge.