What role does a foreign key play in relational databases?

A foreign key plays a crucial role in relational databases by establishing a relationship between tables. This relationship allows for the creation of links between records in different tables, enabling the database to maintain referential integrity. When one table includes a foreign key that points to the primary key of another table, it signifies that the data in one table is related to the data in another, which is essential for designing normalized databases that reduce data redundancy and improve data integrity.

For example, consider a database with a "Customers" table and an "Orders" table. The "Orders" table may have a foreign key that references the "CustomerID" from the "Customers" table. This setup indicates that each order is associated with a specific customer, allowing queries to combine data from both tables effectively.

The other options describe elements that do not correctly convey the specific function of a foreign key in a relational database context. The replication of data or the unique identification of rows pertains to different aspects of database design and relationships, while physical ordering of records refers to how data is stored on disk rather than the logical relationships among the data.