A CDN serves your web pages from its servers to near geographic locations of the end user. If your server located in US and a user opened your site in India it will take some time to directly fetch your web pages from US to India. A CDN stores your site web pages on their server and distributes across their network of servers worldwide, and delivers the webpage when a nearer user request web page. It saves loading times and as well as bandwidth of your hosting.
This simple infograph explains What is CDN? how it works and popular CDN services available to speed up your site.
Now, we think you know the meaning of CDN. If you have any further queries, please feel free to leave a comment.