A cluster is a group of servers or nodes working together within a network as a system to perform specific tasks.
Clusters are scalable and highly available as failed nodes are quickly replaced by hot standby nodes to complete the workload or task. This means that downtime is minimized and the program the cluster works for is consistently accessible. Backup nodes exist to replace primary node if the primary node goes offline which protects data and allows for continuous operations.
As a cluster, nodes load balance their workloads evenly to prevent overloading. Furthermore, parallel processing for complex tasks are possible as nodes can complete sub-tasks in a parallel fashion which reduces processing time.