Content delivery networks (CDNs) are composed of "edge cache" servers that are strategically placed around the world at key Internet network points.  These "edge cache" servers can be used to cache and deliver all types of content – including images, videos, CSS and JavaScript files.

Using a CDN can significantly improve a website's end-user performance, since it enables browsers to more quickly retrieve and download content.  For example, instead of having a browser request for an image traverse all the way across the Internet to your web server to download, a CDN can instead serve the request directly from a nearby "edge cache" server that might only be a single network hop away from your customer (making it return much faster – which makes your pages load quicker).