Final answer:
Referential integrity ensures related data exist in parent table before entry into child table.
Step-by-step explanation:
Referential integrity ensures that related data exist in a parent table before allowing an entry into a child table. It is a feature provided by SQL to maintain the consistency and accuracy of data in a relational database. Referential integrity is enforced using foreign key constraints that define a relationship between tables. When a foreign key constraint is applied, it ensures that any value entered into the child table must already exist in the parent table.