A cluster computer consists of multiple connected nodes that work together like a single system. It can increase performance over a single computer by distributing work across nodes. There are different types of clusters, including load balancing clusters for high performance computing, visualization clusters with graphics cards, and grids that pool multiple distributed resources. Key advantages of clusters are increased performance through parallel processing, scalability by adding nodes, and lower cost by using commodity hardware. Performance monitoring is important as a cluster's speed depends on its nodes and network connection.