The Drive Encryption product settings policy has a "Enabled" checkbox. This box determines whether the system is in an 'active' or 'inactive' state based on whether it is checked or not.
Active = The system has completed policy enforcement and currently has a policy set to enabled (checked). An active system can be encrypted or decrypted depending on policy settings.
Inactive = The system has completed policy enforcement and currently has a policy set to disabled (unchecked). This also means the system is decrypted.
unknown = Either MDE is not installed on the system or it is installed and policy enforcement has not yet completed.