What defines a primary key in a database?

A primary key is defined as a unique identifier for each record in a database table. This uniqueness is crucial because it ensures that each entry can be distinguished from all others, preventing duplicate records and maintaining data integrity. A primary key typically consists of one or more columns that contain unique values, which allows for precise identification of each record in queries and relationships with other tables.

The other options fall short of encapsulating the true definition of a primary key. For instance, while a foreign key serves to link two tables by referencing a primary key from another table, it does not act as a unique identifier for records within its own table. Multimedia content storage, and methods for data organization, do not pertain to the definition of primary keys, as they refer to different aspects of database functionality and structure. Thus, the uniqueness and role of a primary key in ensuring that each record in the table can be accurately identified underscore why the first option is the correct answer.