In computing, a cluster refers to a group of computers or servers that work together so that, in many respects, they can be viewed as a single system. The components of a cluster are usually connected through fast local area networks. Each node (the name of a single computer within the cluster) runs its instance of an operating system. In most circumstances, all of the nodes use the same hardware and the same operating system, although in some setups (i.e. "mixed-match" clusters), different operating systems can be used on each computer or different hardware. 
Clusters are typically used to achieve high availability for critical resources, provide greater computational power for tasks requiring high processing capabilities, or facilitate larger storage solutions via a distributed file system.
Cluster computing can significantly enhance fault tolerance. If one node in the cluster fails, one or more nodes are ready to take its place. This redundancy of nodes is often called failover. Load balancing is also an essential feature of clustering. Load balancing distributes workloads across multiple nodes to optimize resource use, maximize throughput, minimize response time, and avoid overload.
Here are the advantages and disadvantages of clusters in computing:
- Increased availability: If one node fails, other nodes can take over.
- Scalability: New hardware can be easily added as the demand for processing power increases.
- Cost-effectiveness: It is often cheaper to create a cluster of several low-end machines than a single high-end machine with comparable speed.
- Improved performance: Tasks are distributed among different nodes, speeding up processing times.
- Complexity: Setting up a cluster can be complicated. It requires a deep understanding of the underlying technology and the software involved.
- Increased maintenance: As more nodes mean more components, there's a higher chance of hardware failure.
- Single point of failure: Some clustered setups might still have a single point of failure, like shared storage or the network switch.
One example of a cluster system is Google's computing environment, where many computing tasks are managed across a vast cluster of servers to support operations like search, Gmail, and Google Docs.