ELB Target Health is an AWS feature that monitors the health of registered targets in a load balancer. It checks the status of each target and determines if it's healthy or unhealthy. If an unhealthy target is detected, ELB will stop sending traffic to it until the health check returns with a result indicating that the target is healthy again. ELB Target Health can be used to help ensure optimal performance and availability for applications running on AWS. The system helps ensure that only healthy targets receive requests from users, thus reducing latency and improving availability for users. Furthermore, by monitoring target health, ELB can automatically scale out or in based on changes in application demand or resource utilization.