Final answer:
In database systems, a relationship is a link between tables that defines how data are associated with each other, usually facilitated by common keys.
Step-by-step explanation:
A database relationship is a(n) link between tables that define how the data are related. The correct answer to the question is 'd) link'. In the context of databases, a relationship establishes how one table's data corresponds to data in another table, oftentimes through a common key or field.
For example, an 'employees' table could be linked to a 'departments' table through a department ID that appears in both tables. This type of linkage ensures data consistency and supports complex queries that span across multiple tables.