Pre-planned enhancement to the standard SAP system.
SAP anticipates potential customer requests not already implemented in the standard system by predefining them as 'empty modification modules'. Customers fill these modules with their own logic according to their own requirements.
SAP creates customer exits with transaction SMOD. From these customer exits, customers then use transaction CMOD to choose the enhancements they want to process, assign them to enhancement projects, edit the components, and activate the relevant projects.
Using customer exits guarantees upwards compatibility. This is because jumps to exits are predefined in the standard software and the validity of the call interface are both retained, even in future release upgrades.