CDN Content Delivery Network
A geographically distributed network of servers that delivers content from the one closest to the visitor.
When someone in Sydney visits your Swedish site, you don't want all the images to travel all the way from Stockholm. A CDN caches them on a server in Sydney so they're delivered in 10 ms instead of 250.
Popular providers: Cloudflare, Fastly, AWS CloudFront, Bunny.net. Many offer free tiers for small sites.