Google's set of measurable page experience metrics: how quickly the main content appears, how fast the page responds to the first interaction, and how much the layout shifts while loading.
They are a ranking signal and, more importantly, a proxy for whether the site feels broken. Poor scores correlate directly with bounce rate, and they are measured on real visitors, not in a lab.
We measure field data, not just a local score, budget image and script weight from the design stage, and reserve space for images and embeds so content does not jump as the page loads.