Standard SAP sends out or receives in data through IDocs using standard delivered Segments, Message Types and fields. But sometimes, these fields are not sufficient for a specific end-to-end business scenario as far as data transfer is concerned. So in such scenarios, we can add new segments with completely new structures to the standard IDoc as an extension. We create a brand new structure and insert it into existing delivered IDoc structure creating a whole new IDoc satisfying the requirement. This new IDoc is called an Extended IDoc
An IDoc is the run−time instance of an IDoc type. An IDoc consists of a control record, several data records,and a list of status records. The control record defines control information such as sender and receiver information. The data records contain the application data that is to be transferred via IDocs. The status records contain status information (success or failure) recorded at each point in the process.