What is a load balancer and why is it needed?

A load balancer distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed. Benefits: improved availability (servers can fail), better performance (distribute load), scalability (add servers easily), health monitoring (route away from unhealthy servers). Types: hardware (F5), software (Nginx, HAProxy), cloud (AWS ALB/NLB). Algorithms: round-robin, least connections, IP hash. Essential component for any scalable web application.