This document discusses several key SAP concepts:
Functional modules are procedures that can be called from all programs and are defined outside of classes. User exits allow custom programs to be called from specific points in SAP programs and can be viewed using transaction codes SMOD and CMOD. BADIs are templates for enhancement objects that can be called from ABAP programs. BAPIs provide standardized access to SAP business objects and processes and form the basis for integration with external systems.