A DataSource is the object containing all the metadata to bring data from an external system to SAP BW. SAP delivers a list of standard DataSources to bring data from SAP ERP to BW. Other types of DataSources can bring data in from flat files, external databases, …
The data loads are launched by means of an InfoPackage, which triggers the necessary programs in BW and SAP/other source systems to transfer the data to BW.