MongoDB is a popular open-source NoSQL database designed for handling unstructured and semi-structured data. It stores data in a flexible, JSON-like format called BSON, allowing for dynamic schema changes and the ability to handle large, complex datasets. MongoDB excels in scalability and performance, making it ideal for modern applications that require high availability, distributed architecture, and horizontal scaling. Its flexibility, ease of use, and ability to manage large volumes of diverse data make it a go-to solution for big data, real-time analytics, and cloud-native applications.