What is Web Performance?
The discipline of making pages load and respond fast enough that users don't notice the wait.
Definition
Web performance is measured in user-perceived terms rather than server timings: Largest Contentful Paint for when the main content appears, Interaction to Next Paint for responsiveness to input, and Cumulative Layout Shift for visual stability—the three Core Web Vitals Google folds into ranking signals. The dominant costs on modern sites are JavaScript bundle size, render-blocking resources, unoptimized images, and third-party scripts, which is why code splitting, lazy loading, modern image formats, and a CDN deliver most of the available wins. Measurement should combine lab tools (Lighthouse, WebPageTest) for reproducible diagnosis with real-user monitoring for what users actually experience across the long tail of devices and networks. Performance is a regression-prone property, so budgets enforced in CI matter more than one-off optimization sprints.