In the “summary_page” dataset, what does “fullyLoaded” represent? The page load time of a web page?
It refers to the load event AKA onload. Keep in mind that pages that do a lot of work asynchronously may have a fast onload time but a slow user experience, so there isn’t a great representation of page load time unless you know how the site you’re measuring was built. Another disclaimer about the metric is that it’s measured synthetically using WebPageTest so it may not be representative of the many ways users access and load the page and results will vary.
More info about reliability of timing metrics in HTTP Archive: https://httparchive.org/faq#how-accurate-is-the-data,-in-particular-the-time-measurements