What role does a foreign key play in a relational database?

A foreign key is a critical aspect of relational databases, serving the primary purpose of establishing a connection between two tables. It does this by linking the data in one table to the data in another, effectively creating a relationship between the two. This means that a foreign key in one table refers to a primary key in another table, allowing for the management of data across different tables while maintaining referential integrity.

When a foreign key is implemented, it ensures that the values in a column match the values in another table's primary key column, thus enforcing consistency and preventing orphaned records. For instance, if you have a table containing customer information and another table detailing orders, the foreign key in the orders table can reference the primary key in the customers table. This relationship simplifies the retrieval of related data, facilitates complex queries, and helps maintain organized data structures within the database.

While the other options touch on aspects of database structure, they do not accurately describe the specific role of a foreign key. A primary key uniquely identifies a record in its own table, but a foreign key's main function is to create relationships, making the second option the correct choice.