All Apps have an underlying entity (with the same name), which is a data workspace that holds all your data for a given use case (from one or more data sources), this can include initial, intermediate (Embeddings) and results data.
The App user interface sits on top of the newly created Entity and allows for testing and experimentation through drag and drop and linking to test files.
Entities can be accessed directly through the Entities tab and can be queried through the SQL and Query builder interfaces, whether directly or through the App UI.
All Apps have an entity, but not all Entities are Apps. Entities that are created directly are not accessible through the App UI.