These are the terms used in this documentation.
Cluster: A cluster is a group of two or more servers working together to provide applications or services to clients. A cluster provides failover support should a server in the cluster fail. Responder can use a cluster to provide failover support for the Responder services (i.e., Data Services, Archive Services, Prediction Services). A cluster may also be referred to as a server cluster.
Cluster Group: Each virtual server in the cluster is represented by a cluster group. When failover occurs, the entire group will failover.
Resource: Each cluster group consists of resources that indicate information such as physical address, IP address, message queuing and network name.
Node: A node represents a physical server in the server cluster. The names of your nodes can correspond with the names of the servers they represent.