BAPI - Overview

BAPI – Business Application Interface.
BAPI’s are defined in business object repository as methods on SAP business Objects.
These are enables the object oriented view on R/3 application modules and thus basis for the R/3 business frame work development. Because of their open and defined interfaces, these are also used by other applications like Visual Basic etc.
To check BAPI based application wise you need to use the T.code called BAPI.
Here you can find the information of all the BAPI’s by Application area.
Example:
Like if you are looking for a BAPI for Sales Order change in Sales and Distribution area, then, In left side pane Go to Sales and Distribution à Sales à ChangeFromData (method)
Will get the function module BAPI_SALESORDER_CHANGE, always BAPI function modules are Remote enabled and used in events.

You can see the Documentation for this on Documentation tab.

The BAPI does not run a database Commit, which means that the application must trigger the Commit so that the changes are read to the database. For doing this we have to use another BAPI function module, BAPI_TRANSACTION_COMMIT BAPI.