CDN stands for Content Delivery Network. A CDN is an infrastructure composed of many web servers. The largest CDN have thousands of servers worldwide.
The CDN goal is to accelerate the delivery of different web contents and to reduce visitor waiting times. This is achieved through high performance servers, large bandwith and worlwide coverage.
CDN services are used by publishers and ecommerce sites for hosting and delivering images and videos. CDN are also used by ad networks to deliver creatives (images, flash files, video,etc.) and reduce ad serving latency.
CDN explained by Accu Webhosting