A multi-model database is a type of database management system that supports multiple data models within a single integrated platform. These data models can include relational (tables), document (key-value pairs or JSON-like documents), graph (nodes and edges), and other models such as object-oriented or time-series.

OrientDB fits into the category of multi-model databases by offering support for multiple data models, including:

Document Model : OrientDB allows you to store and retrieve data in flexible, schema-less documents similar to other NoSQL document databases like MongoDB. This model is suitable for handling semi-structured data and evolving schemas.

Graph Model : OrientDB provides native support for managing graph data, making it highly efficient for storing and querying highly interconnected data structures. It offers features such as vertices, edges, and property graphs, along with advanced graph algorithms and traversal capabilities.
Object Model : While not as prominent as document and graph models, OrientDB also supports an object-oriented model. This allows you to define classes and objects with properties and methods, making it suitable for applications where object-oriented programming paradigms are preferred.

By supporting multiple data models within a single database instance, OrientDB offers developers the flexibility to choose the most suitable model for their application requirements. This versatility makes OrientDB well-suited for a wide range of use cases, including content management systems, social networks, recommendation engines, real-time analytics, and more.