Short definition
Page speed is how quickly a webpage becomes useful to a visitor, measured in seconds from initial request to interactive.
In depth
Page speed is a user-experience metric, an SEO ranking factor, and a conversion driver. Every additional second of load time on mobile typically costs 7–10% of conversions. Optimizing speed touches every layer: server response time, asset weights, code splitting, third-party scripts, image formats, fonts, and CDN configuration. Modern target: First Contentful Paint under 1.8s, fully interactive under 3.5s on a 4G connection.
Example
A landscaping site removes three unused tracking scripts and lazy-loads below-fold images. Mobile load time drops from 5.2s to 1.9s; bounce rate falls 24 points.