A CDN (Content Delivery Network) is a globally distributed network of edge servers that cache static assets (and increasingly dynamic responses) and serve them from the location closest to each user. Cloudflare, Fastly, AWS CloudFront, Vercel Edge Network, and Akamai are the dominant providers.
The two compounding wins: latency (the user-to-edge round-trip is shorter than user-to-origin), and origin offload (cached requests never hit the origin, dramatically lowering origin server load). Modern CDNs also terminate TLS, run edge functions (Workers, Edge Functions, Lambda@Edge), perform image optimisation, and handle DDoS scrubbing.
For BeaverCheck audits, sites behind a CDN typically post 30-50% better TTFB than direct-origin sites. Pair the CDN with appropriate Cache-Control headers (long TTLs for hashed-filename assets, shorter for HTML) to maximise hit rate.