Initially, there are three Core Web Vitals. The metrics that make up Core Web Vitals will evolve over time, but the current set for 2021 focuses on three aspects of the user experience – loading, interactivity, and visual stability – and includes the following metrics (and their respective thresholds):
Largest Contentful Paint: This is the time it takes for a page’s main content to load. An ideal LCP measurement is 2.5 seconds or faster. What Google is asking here is how fast does the largest piece of content in the viewport take to load? On many websites, this is typically a slider or an image, but it can also be text.
Cumulative Layout Shift: This is the amount of unexpected layout shift of visual page content. You have probably experienced a situation where you’ve loaded a page on your mobile phone, and go to click a button, and at the last second it shifts and you hit something else. This is Cumulative Layout Shift. An ideal measurement is less than 0.1. With this question, Google is asking how quickly is the page stable?