First Contentful Paint (FCP)
FCP measures how long it takes the browser to render the first piece of DOM content after a user navigates to your page.
Your FCP score is a comparison of your page’s FCP time and FCP times for real websites, based on data from the HTTP Archive.
For example, sites performing in the ninety-ninth percentile render FCP in about 1.5 seconds. If your website’s FCP is 1.5 seconds, your FCP score is 99.