HTTP caching is a technique used to speed up the delivery of web content by storing previously requested resources, such as images, scripts, and stylesheets, in a cache.
A web accelerator, such as Varnish, may be used to implement HTTP caching. The usual set up will place the web accelerator between Plone and the Internet. When a request is made to the site, the web accelerator will intercept the request. It then checks to see if it has a cached copy of the requested resource. If a cached copy is found, the accelerator will serve the cached copy directly to the client, else it will make a request to the backend Plone server and then store a copy on the content in its local cache.
HTTP caching and the speed of delivering web content can be improved using a Content Delivery Network (CDN). A CDN is a network of servers located in various geographic regions that work together to deliver web content to users quickly and efficiently. When a user requests a resource from a website that uses a CDN, the request is directed to the closest server in the CDN, rather than having to travel all the way to the website's origin server.