Azure Subscriptions are containers that hold your Resource Groups (RGs) and with that your Resources. It might make sense to have multiple subcriptions for separation of billing or management.
- You can have multiple Subscriptions trust the same Azure Active Directory (AAD)
- Each Subscription can only trust a single directory
- Billing is done per subscription
- Resources can be moved from one Subscription to another if both Subscriptions are in the same AAD Tenant