A CDN(content delivery network) is a system of distributed servers that deliver web content to a user based on his/her geographic location. The two issues that CDN addresses is uptime reliability and the speed of your website.

If a user accesses a regular webpage without CDN, they go directly to the webhost and the webhost serves all the content of the page to the user. This process can be slow if the user is far away from the webhost or if there are a lot of people who are trying to access that page at the same time.

With CDN, a delivery network storage pulls the content from the webhost and distributes it over edge locations. These edge locations are like servers or data centers the are located all across the world. So when a visitor tries to access your website they are redirected to the nearest edge location to load files such as images, videos, etc.

Hence all the traffic get offloaded from your webhost to the CDN which results in higher uptime and more speed. This is why every company who creates a website to deal with their customers should use CDN.