What does referential integrity in a relational database ensure?

Referential integrity in a relational database ensures consistency between linked tables. It is a fundamental aspect that maintains the relationships between tables by enforcing rules that ensure that a foreign key in one table must correspond to a valid primary key in another table. This means that if a record in one table (the parent table) references a record in another table (the child table), the referenced record must exist.

For example, if a database has a table for 'Customers' and another for 'Orders', each order must be linked to a valid customer; thereby, it prevents orphan records in the 'Orders' table if a corresponding customer in the 'Customers' table is deleted or modified without attention to the relational constraints. This integrity constraint protects the logical relationships in the data and preserves the accuracy and validity of the data representation across different tables in the database.

The other options touch on important aspects of database management but do not pertain to referential integrity. For instance, data encryption focuses on security, access controls address user permissions, and data backups are about data recovery, none of which directly relate to maintaining the relationships between tables.