CDN

Content Delivery Network

Geographically distributed caching layer -- Cloudflare, Akamai, CloudFront.

When you'd see it: Web performance and infrastructure. Cloudflare, Akamai, and Fastly are CDNs.

Why it matters: A CDN caches your content on servers around the world so a user loads it from a nearby location instead of your origin. It is the cheapest large win for site speed and a first line of defense against traffic spikes.