A software load balancer is a tool that distributes network traffic across multiple servers to ensure no single server becomes overwhelmed. By managing the flow of requests, it helps improve the performance and reliability of applications, making them more responsive to users. These load balancers can operate on various protocols and are often used in cloud environments. They can also provide features like health checks, which monitor server performance, and automatic scaling, which adjusts resources based on demand. Popular examples include Nginx and HAProxy.