Final answer:
A composite key in database design is a combination of a key from an identifying entity and a unique partial key of its own, used to uniquely identify a record in a relational table.
Step-by-step explanation:
The composite key is the key from the identifying entity plus its own partial key. In database design, a composite key is made up of two or more attributes (columns) that together uniquely identify an entity occurrence (record) in a relational table. For example, in a database that tracks student enrollments, a composite key for the enrollments table could include both the student ID and the class ID, each of which are foreign keys that come from the student table and class table respectively, in addition to a partial key that is unique to the enrollment table.