Anycast routes traffic to the nearest (topologically closest) server sharing an IP address — used by DNS root servers, CDNs, and for DDoS mitigation.
Anycast is why Google DNS (8.8.8.8) responds from a server near you, not a single server. CDNs use anycast to deliver content from the nearest edge. DDoS mitigation: attack traffic is distributed across global nodes, not concentrated at one. One IP, many physical servers worldwide.