This document discusses various metrics for measuring website performance and user experience. It outlines different types of metrics including: - Network metrics like DNS resolution, TCP connection times, and time to first byte. - Browser metrics like start render time, DOM loading/ready times, and page load times. - Resource-level metrics obtained from the Resource Timing API like individual asset load times and response sizes. - User-centric metrics like Speed Index, time to visible content, and metrics for single-page applications without traditional page loads. It emphasizes the importance of measuring real user monitoring data alongside synthetic tests, and looking at higher percentiles rather than just averages due to variability in user environments and network conditions