A Content Delivery Network (CDN) is a system of distributed servers that delivers web content to users based on their geographical location. CDNs improve website performance by caching content closer to users, thereby reducing latency and load times. When a user requests a webpage, the CDN serves the content from the nearest server, resulting in faster access. CDNs also enhance scalability and reliability by distributing traffic, which can prevent server overload during high demand. Additionally, they improve security by providing DDoS (Distributed Denial of Service) protection and optimizing data transfer.