BDC stands for Batch Data Communication and is also referred to as Batch Input. It is a technique for mass input of data where data input into SAP screens is simulated.

BDC was a great way of uploading data into SAP in a pre-BAPI era , now SAP is making available BAPIs for most of the functionalities, some one should first look out for BAPI if it is not available then go for BDC.

Batch Input Session method  still has unmatched error analysis & recovery tool.

Using transaction SHDB it is possible to record transactions as well as create skeleton programs that contain all the necessary code for creating batch input sessions.

https://wiki.sdn.sap.com/wiki/display/ABAP/BDC