Core Web Vitals
Core Web Vitals are three measurements Google uses to judge how a page feels to the person visiting it: how quickly the main content appears, how promptly it responds to input, and how steady the layout stays.
The three values are called Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift. The first measures when the largest visible content is in place. The second, how long the page takes to react to a tap. The third, whether elements shift around while you are already reading.
The measurement happens on real visits with real devices and connections, not in a lab. That is why a site can look flawless on a developer machine and still score badly — what counts is the phone with poor reception, not the desk.
For ranking they are one factor among many, not a lever in themselves. Their real value lies elsewhere: a page that appears late or jumps away under your finger loses visitors before the content ever had a chance.