MongoDB is a popular type of database known for its flexibility and scalability. It falls under the category of NoSQL databases, which means it doesn't use traditional tabular structures like SQL databases. Instead, it stores data in JSON-like documents, making it easier to handle unstructured data. MongoDB is commonly used in applications requiring high performance, real-time analytics, and the ability to scale horizontally. Its flexible schema design allows for rapid development and iteration, making it a preferred choice for modern web and mobile applications.