First paint The time to start of first paint operation. Note that this change may not be visible; it can be a simple background color update or something even less noticeable.
First Contentful Paint (FCP) The time until first significant rendering (e.g. of text, foreground or background image, canvas or SVG, etc.). Note that this content is not necessarily useful or meaningful.
First Meaningful Paint (FMP) The time at which useful content is rendered to the screen.
Largest Contentful Paint (LCP) The render time of the largest content element visible in the viewport.
Speed index Measures the average time for pixels on the visible screen to be painted.
Time to interactive Time until the UI is available for user interaction (i.e. the last long task of the load process finishes).