CDN or a Content Delivery Network is a global network of proxy servers which are located in multiple data centers all around the world. CDN affords better performance to websites and higher availability. It delivers web content to an online user, base on his/hers geographical location. For example, if the website requested is hosted on a server in Germany, but the user that is requesting it is in New Zealand, the closest CDN server will respond to that request.
The CDN makes a copy of the page of the website and caches the content to the different locations of the proxy servers. So when a user requests for this page, the CDN servs the request from the closest proxy server