Wikipedia describes a Content Delivery Network(CDN) as a system of computers containing copies of data, placed at various points in a network so as to maximize bandwidth for access to the data from clients throughout the network. A client accesses a copy of the data near to the client, as opposed to all clients accessing the same central server, so as to avoid bottleneck near that server.

Ecwid uses CDN widely to make the store loading very fast for any customer. 

Ecwid`s CSS and JavaScript code is distributed to lots of servers around the world. When a customer opens your store, he will download CSS and JavaScript from the nearest server. So, if a customer is from the US, the files will be downloaded from a US server. If he is from Europe, a European server will be used. It speeds up loading of your store.

Silver accounts also use Content Delivery Network for product images, it makes Ecwid loading even faster.