"A geographically distributed group of servers which work together to provide faster delivery of Internet content, like websites, videos, and images. A CDN allows for the quick transfer of these assets through a mechanism known as caching. Caching is a way to store a copy of a video, or website page across multiple locations, so that when you try to view it, instead of having to wait to download the entire video, it is already there, saving your computer that download time. The majority of the internet’s traffic is actually distributed through CDN’s. When you watch a video on Netflix or read an article on CNN.com, that content is served from a CDN. Many cloud providers today offer a CDN solution for their customers. Amazon, for example, has CloudFront, Google has Cloud CDN, and Microsoft has Azure CDN."
in other words
A local McDonald's where you can get the same meal regardless of where you are in the world.