A Cluster diagram or clustering diagram is a general type of diagram, which represents some kind of cluster.
A cluster in general is a group or bunch of several discrete items that are close to each other.
The cluster diagram figures a cluster, such as a network diagram figures a network, a flow diagram a process or movement of objects, and a tree diagram an abstract tree.
But all these diagrams can be considered interconnected: A network diagram can be seen as a special orderly arranged kind of cluster diagram.
Specific types of cluster diagrams are: