Caching dramatically speeds up a site.
1. Browser cache
The browser stores CSS, JS, images. Configured via .htaccess Cache-Control.
2. CDN cache
Cloudflare, BunnyCDN — serve from global servers.
3. Server cache (page cache)
Prebuilt HTML saved to disk. For WordPress — WP Rocket, LiteSpeed Cache.
4. Object cache (Redis, Memcached)
Cache DB query results in memory. For high-traffic sites.