What is a foreign key in database normalization?

What is a foreign key in database normalization?

A foreign key in database normalization is a field or a set of fields in a table that refers to the primary key of another table. It establishes a relationship between two tables by ensuring referential integrity and maintaining data consistency. The foreign key constraint ensures that values in the foreign key field(s) must match the values in the primary key field(s) of the referenced table or be null.