Foreign key in DBMS

Definition: Foreign keys are the columns of a table that points to the primary key of another table. They act as a cross-reference between tables.

For example:
In the below example the Stu_Id column in Course_enrollment table is a foreign key as it points to the primary key of the Student table.

Course_enrollment table:

Course_Id	Stu_Id
C01	101
C02	102
C03	101
C05	102
C06	103
C07	102

Student table:

Stu_Id	Stu_Name	Stu_Age
101	Chaitanya	22
102	Arya	26
103	Bran	25
104	Jon	21

Note: Practically, the foreign key has nothing to do with the primary key tag of another table, if it points to a unique column (not necessarily a primary key) of another table then too, it would be a foreign key. So, a correct definition of foreign key would be: Foreign keys are the columns of a table that points to the candidate key of another table.