Business Object Repository (BOR) in an SAP system is a central repository containing all the SAP business object types and SAP interface types along with their respective definitions and methods.
BOR objects can be created/changed/displayed using transaction SWO1 ( Business Object Builder )
Further help and guidance on the Business Object Builder can be found here. [Link to SAP Help]
BOR Objects can be searched for in SAP transports using the following Program ID and object type
A quick how-to on Defining Methods in the BOR Using the BOR/BAPI Wizard is available on the SAP Help site. Click here