A database key is a unique identifier used to distinguish records in a database. It ensures that each entry can be accessed and referenced without confusion. Common types of database keys include the primary key, which uniquely identifies a record, and the foreign key, which links records between different tables. Keys are essential for maintaining data integrity and establishing relationships within a database. For example, in a relational database, a foreign key in one table points to a primary key in another, allowing for organized data retrieval and management. This structure helps in efficiently querying and updating information.