When it comes to back-end development, databases play a vital role in storing and retrieving data efficiently. They serve as a foundation for web applications, enabling users to interact with dynamic content. There are different types of databases, including relational databases and NoSQL databases.

Relational databases are structured databases that store data in tables with predefined relationships. They use SQL (Structured Query Language) to perform operations. For example, consider an e-commerce website where customer data is stored in a relational database. By using SQL queries, we can retrieve specific customer information or generate reports based on certain criteria.

On the other hand, NoSQL databases are non-relational databases that provide flexible data models. They are well-suited for handling large volumes of unstructured or semi-structured data. An example is a social media platform where user data is stored in a NoSQL database, allowing for quick retrieval and modification of user profiles.

The choice of database depends on the specific requirements of the project. Relational databases are often used when data consistency and integrity are crucial, while NoSQL databases are preferred for scalability and high performance.