A computer cluster is a network of connected computers (network nodes). While resources and tasks are shared within the computer network, the user has only a single point of access. The advantage of a computer cluster is that it allows horizontal scaling out.
This refers to increasing the computing power of a cluster by adding more network nodes. This is in contrast to vertical scaling up, where the computing power is increased by buying a more powerful computer.
Computer clusters use the principle of scaling out (horizontal scaling). This circumvents the limits of computing power that exist with single-node computers, as the size of a computer cluster can be increased specifically by adding more nodes.
Because of their scalability, computer clusters have enabled the storage, processing and analysis of Big Data. Without computer clusters, our computing power would be largely tied to the capabilities of single-node servers - a joke considering the demands created by the masses of data out there.