The primary purpose of a database in an application is to store, manage, and retrieve data efficiently. Databases centralize information, enabling applications to perform operations like reading, writing, and querying data quickly and reliably. They support various structures, such as relational databases, which organize data into tables, or non-relational databases, which handle unstructured data. Databases are crucial for ensuring data integrity, security, and availability, allowing applications to provide users with valuable insights and maintain a seamless operational flow.