Final answer:
A foreign key is an attribute that establishes a relationship between two tables in a database.
Step-by-step explanation:
A foreign key is an attribute (or combination of attributes) that references the primary key of another relation. It is used to establish a relationship between two tables in a database. The values of the foreign key must match the values of the primary key in the referenced table, ensuring referential integrity.
For example, consider a database with two tables: 'Students' and 'Courses'. The 'Courses' table has a primary key column called 'Course_ID'. The 'Students' table has a foreign key column called 'Course_ID' that references the primary key in the 'Courses' table. This allows us to relate the student to the course they are enrolled in.