A cluster is a logical way to group end-devices.
An end-device can only be present in one cluster.

This is also where is defined how the LoRa data is pushed to your server. This is a per-cluster setting.

A fleet is a logical way to group gateways.
A gateway can only be present in one fleet.

A station is identified by its EUI.
A station can only be present in one fleet.

Sensor associated to a cluster and a region (868, 915, 923).
Can be activated by OTAA or ABP.

A customer is a group of fleets and clusters.