CDN (content delivery network)
Also called: Edge cache, PoP
Servers in many cities that keep copies of your files and answer users from nearby, fetching from your origin only on a miss.
Definition
Requests go to the nearest edge server; a cache hit answers in milliseconds, a miss is fetched from the origin (often through an origin shield) and stored. Cache-Control headers decide what may be cached and for how long; personal responses must be private. Files are versioned with content hashes in their URLs instead of purged, and private files are served with short-lived signed URLs.
In practice
/assets/app.8d2f1c.js is cached for a year at every edge; a new release references app.9e44a0.js instead.