Foreign key in DBMS

Question

What do you understand by the term foreign key in DBMS, and why is it employed for?

Answer 1

A foreign key is employed to establish relationships among relations in the relational model. Technically, a foreign key is a column (or columns) emerging in one relation which is (or are) the primary key of any other table. Though there might be exceptions, the values in the foreign key columns generally must correspond to values existing in the setup of primary key values. This correspondence requirement is made in a database employing a referential integrity constraint on the foreign key.