What defines the structure of a database, including tables and relationships?

The term that defines the structure of a database, including tables and the relationships between them, is the database schema. A database schema serves as a blueprint for how data is organized within the database, specifying the types of data that can be stored, the relationships between different data entities, and the constraints that apply to the data. This includes not only tables and their fields but also constraints such as primary and foreign keys that dictate how tables relate to one another.

In contrast, a database instance refers to the actual data stored in the database at any given time, which can change as data is added or modified. The database engine is the underlying software that handles the database's data management operations, including querying, updating, and maintaining data integrity. Lastly, a database query is a request for information from the database, formulated using a query language, such as SQL, but does not define the structure itself. Thus, the concept of a database schema is central to understanding how data is organized and interrelated within a database system.