Final answer:
In Oracle 12c, a 'schema' is the correct term for a defined, self-contained structure that includes various database objects associated with a particular user.
Step-by-step explanation:
A database schema is the correct answer to the student's question. In Oracle 12c, a schema is a collection of database objects, including tables, views, stored procedures, and more, associated with a particular user or account. It is a logical structure that defines how the data is stored, organized, and manipulated. An instance refers to the set of Oracle software processes that manage database files, and a cluster is a group of interconnected databases that are treated as a single server. An object is a more generic term that could refer to any item that can be individually managed, such as a table or view in the database.