When you are doing data loads into SAP using BDC, you will typically create Batch Input Sessions and execute them seperately either using the program RSBDCSUB or SM35. This is processing the transactions in batch. You are combining several transactions into one batch and then processing them at a time when the online user activity is low.
Background jobs are any processing that is executed in the background. This is slightly different from batch processing in the sense that it need not have any BDC data processing in it. It can be as simple as a report being executed in the background. Batch processing necessarily involves BDC data.
Hope this helps,
Srinivas
