What does a foreign key in database terminology signify?

A foreign key in database terminology signifies a reference to another table’s primary key. This relationship establishes a link between the data in two tables, enabling the database to maintain referential integrity. When a foreign key is defined in one table, it points to the primary key in another table, allowing for connections between records in both tables.

This mechanism is essential in relational database design, as it ensures that relationships between data are coherent and consistent. For example, if you have a table for customers and another for orders, the orders table may contain a foreign key that references the customer’s primary key. This structure allows for the effective retrieval of data tied to specific customers, which is fundamental in executing JOIN operations in SQL.

The other options do not accurately describe the role of a foreign key. An alternative name for a primary key would simply be a synonym and does not encapsulate the Foreign Key's purpose. A key that unlocks a tuple inaccurately describes database terminology, as "unlocking" is not a concept used in relational databases. Lastly, a key used only for indexing purposes does not capture the relational integrity aspect of foreign keys, as they primarily serve to establish relationships, while indexes are used for improving speed of data retrieval.