Final answer:
A field or group of fields from a weak entity used to complete a key is known as a 'partial key' or 'discriminator'. The partial key is necessary for the unique identification of entries in a weak entity within a database.
Step-by-step explanation:
The term the student is looking for is partial key or discriminator. In the context of databases, particularly in an entity-relationship model, a weak entity is an entity that cannot be uniquely identified by its attributes alone. Therefore, it relies on a foreign key in combination with its attributes to create a primary key, which is known as a partial key. This partial key is composed of the field or group of fields from the weak entity that, when combined with the foreign keys from the related strong entity, uniquely identifies entries in the weak entity.