A device or software that distributes the work between several computers, processes, hard disks, or other resources to get optimal resource utilization. A network load balancer, in the context of Application Request Routing, is a proxy-based load balancer that distributes network traffic among several Web servers.
A Layer-4 (TCP, UDP) type load balancer that distributes incoming traffic among healthy service instances in cloud services or virtual machines defined in a load balancer set.