Cube's open source data modeling language is used to describe measures, dimensions, and relationships in a data source, generating SQL queries against data sources when responding to requests made to the REST, GraphQL, and SQL APIs. The language is decoupled from specific interfaces, visualization, or user experience, allowing consistent definitions across applications. It's based on JavaScript and enables dynamic data definitions, caching, and access control rules through a virtual machine. A data modeling example shows how to represent tables in Cube's modeling language, defining measures, dimensions, and relationships with properties like `sql`, `joins`, and `measures`. The language can be queried using APIs or explored within BI tools, providing a foundation for accessible and consistent data across downstream applications.