Core Web Vitals are Google’s metrics for measuring real-world page experience: loading speed, responsiveness and visual stability. They are Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS). Google uses them as a ranking signal, and they also affect conversion on mobile.
On WooCommerce stores, heavy themes, unoptimised images and third-party scripts are the usual culprits.