Referential integrity is a constraint in database management systems (DBMS) that ensures that all data in a database remains consistent and up-to-date. It is a term used in database design to describe the relationship between two tables. Referential integrity requires that a foreign key must have a matching primary key or it must be null. In other words, it ensures that each foreign key in a table points to a unique primary key value in another table. This constraint is specified between two tables, a parent table and a child table, and it maintains the correspondence between rows in these tables.

Referential integrity is important because it helps to prevent incorrect records from being added, deleted, or modified. It ensures that when changes are made to data in one place, those changes are reflected in other related records. If referential integrity is not enforced, then data redundancy and inconsistencies may occur.

Some best practices for creating referential integrity include creating primary and foreign keys for each table, ensuring that the data types match, ensuring that there are no duplicate entries, and making sure not to create circular relationships.

In summary, referential integrity is a constraint on the database design that ensures that each foreign key in a table points to a unique primary key value in another table, and it helps to prevent incorrect records from being added, deleted, or modified.