The NLS_DATABASE_PARAMETERS shows the values of the NLS parameters for the database. Oracle notes these differences between the parameters.

• NLS_SESSION_PARAMETERS shows the NLS parameters and their values for the session that is querying the view. It does not show information about the character set.
• NLS_INSTANCE_PARAMETERS shows the current NLS instance parameters that have been explicitly set and the values of the NLS instance parameters.
• NLS_DATABASE_PARAMETERS shows the values of the NLS parameters for the database. The values are stored in the database.

SELECT * FROM NLS_SESSION_PARAMETERS ORDER BY 1;   
SELECT * FROM NLS_INSTANCE_PARAMETERS ORDER BY 1;  
SELECT * FROM NLS_DATABASE_PARAMETERS ORDER BY 1; 

The NLS_LANGUAGE and NLS_TERRITORY values in NLS_DATABASE_PARAMETERS cannot be changed once the database has been created

References

dba-oracle
Oracle Blog