A content delivery network (CDN) is a geographically distributed group of servers that work together to provide fast internet content delivery. They achieve this by caching and distributing copies of static content, such as HTML pages, JavaScript files, stylesheets, and images, from a network location closest to the user. This reduces the distance that data has to travel and speeds up the loading of web pages and other online content.

CDNs are essential for today's internet, as they help to reduce latency and improve the user experience. They also provide additional benefits, such as increased security and reduced load on origin servers. Some popular CDN providers include Cloudflare, Amazon CloudFront, and Akamai. 

This makes a content delivery network a crucial component of the internet infrastructure that ensures fast and efficient delivery of web content to users around the world. These are highly recommended because they not only help improve search optimization technically, they also improve user experience and interaction.