Checking or Writing Business Object Documentation 
Procedure
Ascertain whether the business object and its key fields have been documented. You can do this by selecting the Documentation tab in the BAPI Explorer, or directly in the BOR as follows:
If there is no existing documentation for a business object, you must write it using transaction SW01. To write the documentation, when the business object is displayed, choose Display <-> Change, and then choose Goto ® Documentation.
Discuss with your data modeler the exact definition of the business object.
Business objects are objects in the SAP information environment and must be documented in accordance with the standard guidelines on object documentation.

For an example, see
Writing Key Field Documentation
If there is no documentation on a key field, document it as data element documentation. This is described in
Data Element Documentation.