The common fields used in a relationship between tables are called:

The correct option is Key fields.

In relational database management systems (RDBMS), data is stored across multiple tables. To establish connections or relationships between these tables, we use common fields that link rows in one table to rows in another. These common fields are known as key fields.

Key fields serve specific roles in defining relationships:
1. Primary Key: A key field (or set of fields) in a table that uniquely identifies each record in that table.
2. Foreign Key: A key field in one table that references the Primary Key of another table, thereby establishing a logical relationship between them.

Because these linking fields are fundamental keys used to unlock and join related data, they are collectively referred to as key fields. Other terms like "Joint fields," "Main fields," or "Table fields" are not standard database terminology for these relational elements.