Commonly used terms and abbreviations within Grafana Enterprise Metrics documentation are as follows:

Access policyAn access policy is a resource that contains a granular set of permissions which specify what actions a request to GEM is allowed to do. In GEM, access policies are created with the desired set of permissions. Then API tokens can be generated that are associated with a particular access policy. You can also configure GEM to integrate with an OAuth backend to externally generate tokens associated with a particular access policy.
ClusterA cluster is a licensed deployment of Grafana Metric Enterprise. Clusters are uniquely named and must have a corresponding license.
TenantA tenant is scoped to a particular cluster. New samples can be written to a tenant and queries can be issued to a particular tenant. Each tenant will store its metrics in a separate set of TSDB blocks that are stored in the configured storage bucket. The blocks themselves will be stored in the bucket with the name of the tenant as a prefix. This means once a tenant is created, its name cannot be changed. However, the display_name for a tenant can be changed.
TokenA token is a randomly generated string that can be used as an API key when making requests to GEM.

Relationship of GEM terminology