BATCH INPUT SESSION is an intermediate step between internal
table and database table. Data along with the action is
stored in session ie data for screen fields, to which screen
it is passed, program name behind it, and how next screen is
processed.

it is a data transfer technique,it is used in case of huge 
amount of data,for error handling session is automatically 
created with the parameter keep = 'x' for further 
processing in future,it can be process in foreground and 
back ground also,but data updatation must be schynarous only
it is a aschynarnous processing,