What is the role of a Foreign Key in relational databases?

A Foreign Key in relational databases serves as a critical mechanism to establish and enforce relationships between tables. Specifically, it is a field (or a collection of fields) in one table that uniquely identifies a row in another table. This relationship allows for the creation of links between data in different tables, thereby enabling complex queries and data integrity.

In practical terms, the Foreign Key points to the Primary Key of another table. By doing so, it ensures that the value entered in the Foreign Key field corresponds to an existing Primary Key value in the referenced table. This relationship is fundamental for maintaining referential integrity, which means ensuring that the data remains consistent and valid across the database.

The other options do not accurately define the role of a Foreign Key. While a Foreign Key is related to the uniqueness of identifiers, it does not serve as a unique identifier itself—this is the function of a Primary Key. Thus, the correct choice captures the essence and functionality of Foreign Keys in the context of relational databases.