The Management plane interface is used for managing the Key Vault itself which includes operations like creating and deleting key vaults, retrieving key vault properties, and updating access policies.
The data plane is used for working with the data stored in a key vault and includes operations of add, delete, and modify keys, secrets, and certificates.
Access to a key Vault is controlled through these two planes and the applications access these planes through endpoints. Refer to Resource endpoints for details.
The Management plane access is provided through RBAC whereas access to a data plane is provided through Key Vault access policies.
Source: Secure your key vault