Jitterbit Entities are only used in the creation of OData Services. A Jitterbit Entity defines a database or SAP endpoint, a selection of tables, and a selection of fields that provide the data to an OData Services.
Jitterbit Entities are created within a Jitterbit Design Studio project, and a project may contain multiple entities.
Each API Entity Operation is created within and assigned to a Jitterbit Entity. A Jitterbit Entity may be assigned one or more API Entity Operations, but each Entity is limited to only one API Entity Operation per HTTP method.
Jitterbit Entities and API Entity Operations are assigned to OData Services when the APIs are created. See these articles for additional information: