In a relational database, a primary key is sometimes made up of multiple fields. what is this known as?

Foreign key is the correct answer for the above question.

Explanation:

A foreign key is a key that is used to extract the information of a foreign table with the help of primary key value. When there is a normalized table then it needs to split on two or more tables to overcome the problem of normalization. So is there is a two table then the primary key is used for the first table and the combination of the primary key and foreign key is used to identify the record of the foreign table. The foreign key is made up of multiple fields because there is no single field in the foreign which can not be null for any instance of the primary table. It happens when there is data for the primary table but there is no record for the foreign table.The above question wants to ask about the term which is made up of multiple fields which is a foreign key which is described as above. Hence Foreign key is the correct answer for the above question.