A content delivery network (CDN) is a system of distributed servers that deliver web content to a user based on the geographic locations of the user, the origin of the webpage, and a content delivery server.
CDN's are used to improve the performance and availability of websites by serving content from locations closer to the user. This reduces the distance that data has to travel, leading to faster loading times and a better user experience.
Imagine that you are trying to access a website that is hosted in New York from a computer in Sydney. Without a CDN, the data has to travel all the way from New York to Sydney, which can take a long time. With a CDN, the website's content is replicated and stored on servers around the world, so when a user in Sydney accesses the website, the data is served from a nearby server rather than all the way from New York. This speeds up the loading time and improves the user experience.
CDN's are used by many websites and are especially important for sites with a lot of traffic or those that serve content globally. Some popular CDN providers include Akamai, Cloudflare, and Amazon CloudFront.