Final answer:
When data has a unique identifier that is already part of the data, it can be used as a natural primary key, which uniquely identifies each record in a database.
Step-by-step explanation:
Sometimes your data will have a unique identifier that is already a part of your data. When that is true, you can use the field as a natural primary key. A natural primary key is a field that naturally exists in the data, is unique for each record, and can be used to identify each record uniquely without the need for an additional artificially created key. In contrast to composite keys, which are made up of two or more attributes, or foreign keys, which link one table to another, a natural primary key is simple and already exists within the dataset. Primary keys ensure that each record within a table can be uniquely identified and are essential in database design.