Storefront Speed Journal glossary
Largest Contentful Paint (LCP)
The time until the largest visible content element - on storefronts, usually a hero or product image - finishes rendering. Google's 'good' threshold is 2.5 seconds at the 75th percentile of real visits.
Interaction to Next Paint (INP)
A responsiveness metric: the delay between a user interaction (tap, click, keypress) and the next painted frame. Replaced First Input Delay in March 2024. 'Good' is 200 milliseconds or less.
Cumulative Layout Shift (CLS)
A stability metric quantifying how much visible content moves unexpectedly during load. Promo banners and late-loading fonts are common storefront causes. 'Good' is 0.1 or less.
Field data (RUM)
Measurements collected from real visitors' browsers - real user monitoring - as opposed to lab tests. Google's CrUX dataset is the standard public source; ranking systems use field data.
Edge caching
Storing rendered pages or assets on servers geographically close to the shopper, so responses skip the trip to the origin. For dynamic storefronts, full-page edge caching is the biggest single speed lever after script hygiene.
Main thread
The browser thread that runs JavaScript and handles input. When scripts saturate it, pages feel frozen even after they look loaded - the root cause of most poor INP scores.