A load balancer distributes incoming network traffic across multiple servers to ensure no single server becomes overwhelmed. It improves application availability, reliability, and performance. Load balancers can operate at Layer 4 (transport) or Layer 7 (application) of the OSI model. Algorithms include round-robin, least connections, IP hash, and weighted distribution. Cloud providers offer managed load balancers like AWS ELB, Azure Load Balancer, and Google Cloud Load Balancing.