The function of a content delivery network (CDN) in web performance is to optimize the delivery of web content to users globally. A CDN achieves this by caching content on multiple servers located closer to end-users, reducing latency and load times. By efficiently distributing data, CDNs enhance website performance, reliability, and user experience, especially for media-heavy sites. Furthermore, CDNs can provide added security and help manage traffic spikes during times of high demand, ensuring consistent service availability.