Global Server Load Balancing (GSLB) refers to load balancing implemented at the DNS level.
DNS query results are customized in order to direct clients to the geographically closest backend server or load balancing endpoint where the requested web service can be accessed. This reduces the content delivery time (connection latency) to clients and improves user interactivity and experience with web services. When incorporated with health checks, GSLB can help to implement high availability geographical redundancy.