What is a lookup field in Access primarily used for?

A lookup field in Access is primarily used to select a value from a related table. This functionality allows users to create a more user-friendly experience when entering data into forms or tables. Instead of manually typing in a value, users can choose from a predefined list that pulls data from another table. This ensures data consistency and integrity by reducing the likelihood of errors and making it easier to enforce relationships between tables in the database.

For example, if you have a database for a bookstore, a lookup field could be used to allow users to select an author from a list of authors stored in a separate table. This simplifies the process for the user and ensures that the data entry conforms to existing records.

The other options do not accurately capture the primary function of a lookup field. While storing large amounts of data is characteristic of fields in general, lookup fields specifically facilitate value selection. Automatically calculating values is a feature of calculated fields, and defining complex queries pertains to query design rather than to the function of lookup fields.