Answer : External level Data hiding
We have 3 form of Schema
Physical
Conceptual
External
External Data Level
In the relational model, the external schema also presents data as a set of relations. An external schema specifies a view of the data in terms of the conceptual level. It is tailored to the needs of a particular category of users. Portions of stored data should not be seen by some users and begins to implement a level of security and simplifies the view for these users
Examples:
Students should not see faculty salaries.
Faculty should not see billing or payment data.
Reference : Three Level Database Architecture explanation is here