A candidate key is a set of one or more columns that can uniquely identify a row within a table in a relational database. It is a minimal superkey, meaning that it is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column could produce duplicate combinations of values. A table can have multiple candidate keys, each with a different number of attributes. Specific candidate keys are sometimes called primary keys, secondary keys, or alternate keys. The primary key is used as the official unique identifier for a row within the table. The value of the candidate key is unique and may be null for a tuple. Every table must have at least a single candidate key. The candidate key can be simple (having only one attribute) or composite (having multiple attributes) . The candidate key plays a vital role in maintaining the integrity and consistency of a database by ensuring that each row within a table is unique and can be identified independently.