Which definition best describes a primary key?

A primary key is fundamentally a field or set of fields within a database table that provides a unique identifier for each record in that table. This uniqueness ensures that no two records can share the same primary key value, which is crucial for maintaining data integrity and avoiding ambiguity when retrieving records.

While the other options contain elements that relate to database concepts, they do not encapsulate the full definition of a primary key appropriately. Saying it is a unique identifier for a table does not specify the role it plays in individual records, which is why the chosen answer is more precise. Furthermore, fields that can contain duplicate values are specifically excluded from being primary keys, as duplicates would negate the core function of ensuring uniqueness. A column that relates to another table is more indicative of foreign keys, which serve to establish relationships between different tables rather than uniquely identify records within a single table. Thus, the definition highlighting the unique identification of a record within a table captures the essence of what a primary key is designed to do.